GLES: Small cleanups

Scissor the stencil readback to the region actually being read back - latent,
every caller passes a zero origin today.

Remove a DecodeVerts call that can never do anything: both branches above it
have already advanced decodeVertsCounter_ to numDrawVerts_. Worse than useless,
since in the non-skinning branch the vertices went to the push buffer, so
decoded_ doesn't hold them.

GPU/GLES/DrawEngineGLES.cpp

@@ -292,7 +292,6 @@ void DrawEngineGLES::Flush() {
 		int vertexCount;
 		int maxIndex;
 		bool useElements;
-		DecodeVerts(dec_, decoded_);
 		DecodeIndsAndGetData(&prim, &vertexCount, &maxIndex, &useElements, false);
 		gpuStats.perFrame.numVertsDrawn += vertexCount;
 

GPU/GLES/StencilBufferGLES.cpp

@@ -136,7 +136,9 @@ bool FramebufferManagerGLES::ReadbackStencilbuffer(Draw::Framebuffer *fbo, int x
 	draw_->BindSamplerStates(TEX_SLOT_PSP_TEXTURE, 1, &stencilReadbackSampler_);
 
 	// We must bind the program after starting the render pass.
-	draw_->SetScissorRect(0, 0, w, h);
+	// Note: scissor to the region we're about to read back, not to (0, 0, w, h) - every caller
+	// passes (0, 0) today, but with a nonzero origin the copy below would read scissored-away pixels.
+	draw_->SetScissorRect(x, y, w, h);
 	draw_->BindPipeline(stencilReadbackPipeline_);
 
 	// Fullscreen triangle coordinates.