Prevent bit shifting if num bits is negative

Causes OpenGL Software Renderer to generate incorrect window
coordinates on MIPS & possibly x86

Change-Id: I3c51b6a5a4e6af75e9b31d9d47e4e4d894825888
Signed-off-by: Bhanu Chetlapalli <bhanu@mips.com>

libpixelflinger/fixed.cpp

@@ -62,7 +62,8 @@ int32_t gglRecipQ(GGLfixed x, int q)
     int shift;
     x = gglRecipQNormalized(x, &shift);
     shift += 16-q;
-    x += 1L << (shift-1);   // rounding
+    if (shift > 0)
+        x += 1L << (shift-1);   // rounding
     x >>= shift;
     return x;
 }