Fix missed yield in xTaskResumeFromISR (#207)

If a higher priority task than the currently running task was resumed
using xTaskResumeFromISR and the user chose to ignore the return value
of xTaskResumeFromISR to initiate a context switch using
portYIELD_FROM_ISR, we were not doing the context switch on the next run
of the scheduler. This change fixes this by marking a yield as pending
to ensure that the context switch is performed on the next run of the
scheduler.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

tasks.c

@@ -1949,6 +1949,11 @@ static void prvAddNewTaskToReadyList( TCB_t * pxNewTCB )
                     if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
                     {
                         xYieldRequired = pdTRUE;
+
+                        /* Mark that a yield is pending in case the user is not
+                         * using the return value to initiate a context switch
+                         * from the ISR using portYIELD_FROM_ISR. */
+                        xYieldPending = pdTRUE;
                     }
                     else
                     {