fix [3018216] UI shrinks / stretches while using apps with IME

Change-Id: Ie4c5d8a434b4489355ed8c52af96eb931b4d7167
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 833181b..1b21a8d 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -367,6 +367,7 @@
         Mutex::Autolock _l(mLock);
 
         // zero means default
+        const bool fixedSize = reqWidth && reqHeight;
         if (!reqFormat) reqFormat = mFormat;
         if (!reqWidth)  reqWidth = mWidth;
         if (!reqHeight) reqHeight = mHeight;
@@ -380,7 +381,7 @@
             mReqWidth  = reqWidth;
             mReqHeight = reqHeight;
             mReqFormat = reqFormat;
-            mFixedSize = reqWidth && reqHeight;
+            mFixedSize = fixedSize;
 
             lcblk->reallocateAllExcept(index);
         }