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>
diff --git a/tasks.c b/tasks.c
index 94b3e1f..62ab95a 100644
--- a/tasks.c
+++ b/tasks.c
@@ -1949,6 +1949,11 @@
                     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

                     {