Fix doFadingAnimationLocked in sanitized builds.

The loop as constructed causes i to overflow twice when i = 0 on integer
overflow sanitized builds.

 runtime error: unsigned integer overflow: 0 - 1 cannot be represented
 in type 'size_t' (aka 'unsigned long')

 runtime error: unsigned integer overflow: 18446744073709551615 + 1
 cannot be represented in type 'size_t' (aka 'unsigned long')

This refactors the loop to avoid the overflows.

Bug: 30969751
Test: Compiles, device boots, enabled pointer location overlay.
Change-Id: I844bb3b84b1f536c50d06fb489fcc22590d4aa98
Merged-In: I844bb3b84b1f536c50d06fb489fcc22590d4aa98
(cherry picked from commit 7ee0dba095)

libs/input/PointerController.cpp

@@ -551,18 +551,20 @@ bool PointerController::doFadingAnimationLocked(nsecs_t timestamp) {
     }
 
     // Animate spots that are fading out and being removed.
-    for (size_t i = 0; i < mLocked.spots.size(); i++) {
+    for (size_t i = 0; i < mLocked.spots.size();) {
         Spot* spot = mLocked.spots.itemAt(i);
         if (spot->id == Spot::INVALID_ID) {
             spot->alpha -= float(frameDelay) / SPOT_FADE_DURATION;
             if (spot->alpha <= 0) {
-                mLocked.spots.removeAt(i--);
+                mLocked.spots.removeAt(i);
                 releaseSpotLocked(spot);
+                continue;
             } else {
                 spot->sprite->setAlpha(spot->alpha);
                 keepAnimating = true;
             }
         }
+        ++i;
     }
     return keepAnimating;
 }