Fix a hang in SF caused by invalid transform matrix from the WM

WindowManager could create by transforms because of divide by zero.

Bug: 5422468
Change-Id: I782f87ebb78b5ff23750e22837f36ca6cfed1f2f

Author: pixelflinger

services/java/com/android/server/wm/WindowState.java

@@ -1120,7 +1120,11 @@ void computeShownFrameLocked() {
                 // window's center).
                 final float w = frame.width();
                 final float h = frame.height();
-                tmpMatrix.setScale(1 + 2/w, 1 + 2/h, w/2, h/2);
+                if (w>=1 && h>=1) {
+                    tmpMatrix.setScale(1 + 2/w, 1 + 2/h, w/2, h/2);
+                } else {
+                    tmpMatrix.reset();
+                }
             } else {
                 tmpMatrix.reset();
             }