Only zero alpha if stencil op consistently says to zero.

Otherwise we may be better off keeping the alpha.

GPU/GLES/FragmentShaderGenerator.cpp

@@ -174,7 +174,11 @@ StencilValueType ReplaceAlphaWithStencilType() {
 			return STENCIL_VALUE_UNIFORM;
 
 		case GE_STENCILOP_ZERO:
-			return STENCIL_VALUE_ZERO;
+			if (gstate.getStencilOpZFail() == GE_STENCILOP_ZERO) {
+				return STENCIL_VALUE_ZERO;
+			} else {
+				return STENCIL_VALUE_KEEP;
+			}
 
 		// Decrementing always zeros, since there's only one bit.
 		case GE_STENCILOP_DECR: