Fix some node timing errors.

This commit fixes a bug relating to nodes with a scheduled start/stop
time. Whether or not the node is considered started or stopped is being
incorrectly reported by `ma_node_get_state_by_time_range()`.

Another issue is fixed in `ma_node_read_pcm_frames()`, which is related
to the fix above, where the frame count can underflow thereby resulting
in a crash.

Public issue https://github.com/mackron/miniaudio/issues/969

miniaudio.h

@@ -74965,12 +74965,12 @@ MA_API ma_node_state ma_node_get_state_by_time_range(const ma_node* pNode, ma_ui
     its start time not having been reached yet. Also, the stop time may have also been reached in
     which case it'll be considered stopped.
     */
-    if (ma_node_get_state_time(pNode, ma_node_state_started) > globalTimeBeg) {
+    if (ma_node_get_state_time(pNode, ma_node_state_stopped) < globalTimeBeg) {
-        return ma_node_state_stopped;   /* Start time has not yet been reached. */
+        return ma_node_state_stopped;   /* End time is before the start of the range. */
     }
 
-    if (ma_node_get_state_time(pNode, ma_node_state_stopped) <= globalTimeEnd) {
+    if (ma_node_get_state_time(pNode, ma_node_state_started) > globalTimeEnd) {
-        return ma_node_state_stopped;   /* Stop time has been reached. */
+        return ma_node_state_stopped;   /* Start time is after the end of the range. */
     }
 
     /* Getting here means the node is marked as started and is within its start/stop times. */
@@ -75050,14 +75050,14 @@ static ma_result ma_node_read_pcm_frames(ma_node* pNode, ma_uint32 outputBusInde
         return MA_INVALID_ARGS; /* Invalid output bus index. */
     }
 
+    globalTimeBeg = globalTime;
+    globalTimeEnd = globalTime + frameCount;
+
     /* Don't do anything if we're in a stopped state. */
-    if (ma_node_get_state_by_time_range(pNode, globalTime, globalTime + frameCount) != ma_node_state_started) {
+    if (ma_node_get_state_by_time_range(pNode, globalTimeBeg, globalTimeEnd) != ma_node_state_started) {
         return MA_SUCCESS;  /* We're in a stopped state. This is not an error - we just need to not read anything. */
     }
 
-
-    globalTimeBeg = globalTime;
-    globalTimeEnd = globalTime + frameCount;
     startTime = ma_node_get_state_time(pNode, ma_node_state_started);
     stopTime  = ma_node_get_state_time(pNode, ma_node_state_stopped);
 
@@ -75070,11 +75070,16 @@ static ma_result ma_node_read_pcm_frames(ma_node* pNode, ma_uint32 outputBusInde
     therefore need to offset it by a number of frames to accommodate. The same thing applies for
     the stop time.
     */
-    timeOffsetBeg = (globalTimeBeg < startTime) ? (ma_uint32)(globalTimeEnd - startTime) : 0;
+    timeOffsetBeg = (globalTimeBeg < startTime) ? (ma_uint32)(startTime - globalTimeBeg) : 0;
     timeOffsetEnd = (globalTimeEnd > stopTime)  ? (ma_uint32)(globalTimeEnd - stopTime)  : 0;
 
     /* Trim based on the start offset. We need to silence the start of the buffer. */
     if (timeOffsetBeg > 0) {
+        MA_ASSERT(timeOffsetBeg <= frameCount);
+        if (timeOffsetBeg > frameCount) {
+            timeOffsetBeg = frameCount;
+        }
+
         ma_silence_pcm_frames(pFramesOut, timeOffsetBeg, ma_format_f32, ma_node_get_output_channels(pNode, outputBusIndex));
         pFramesOut += timeOffsetBeg * ma_node_get_output_channels(pNode, outputBusIndex);
         frameCount -= timeOffsetBeg;
@@ -75082,6 +75087,11 @@ static ma_result ma_node_read_pcm_frames(ma_node* pNode, ma_uint32 outputBusInde
 
     /* Trim based on the end offset. We don't need to silence the tail section because we'll just have a reduced value written to pFramesRead. */
     if (timeOffsetEnd > 0) {
+        MA_ASSERT(timeOffsetEnd <= frameCount);
+        if (timeOffsetEnd > frameCount) {
+            timeOffsetEnd = frameCount;
+        }
+
         frameCount -= timeOffsetEnd;
     }