sf: Validate display id while introducing 50ms delay

Correct condition check while validating display id while
introducing 50ms delay when external animation is disabled.

Change-Id: I625857133582d2d31560d36421a49fdb865b8f86
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 0d5f579..e379bf6 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2340,7 +2340,8 @@
     if(mDisableExtAnimation) {
         for (size_t i=0 ; i<count ; i++) {
             const DisplayState& s(displays[i]);
-            if(s.token != mBuiltinDisplays[DisplayDevice::DISPLAY_PRIMARY]) {
+            if((mDisplays.indexOfKey(s.token) >= 0) && (s.token !=
+                    mBuiltinDisplays[DisplayDevice::DISPLAY_PRIMARY])) {
                 const uint32_t what = s.what;
                 // Invalidate and Delay the binder thread by 50 ms on
                 // eDisplayProjectionChanged to trigger a draw cycle so that