Add an argument check for compressed formats in glCompressedTexSubImage2D

The implementation of OpenGLES_v2 glCompressedTexSubImage2D() API
lacks of a sanity check for compressed formats. When a
non-compressed format is specified (e.g. GL_RGB), an unreachable
condition of SS's internal function, ComputeCompressedSize(), is
hit.

This patch is to add a check in CompressedTexSubImage2D() function
to prevent invalid formatd from being entered, in terms of
OpenGL_v2 API integrity in accordance with Khorons's specification

Bug: b/116776984
Test: Manual tests using OGLESHelloAPI by specifying GL_RGB format
Change-Id: Icc964ecb9dbbdef6c6bc82dab42c35290917159e
Reviewed-on: https://swiftshader-review.googlesource.com/c/21548
Reviewed-by: Merck Hung <merckhung@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Merck Hung <merckhung@google.com>

src/OpenGL/libGLESv2/libGLESv2.cpp

diff --git a/src/OpenGL/libGLESv2/libGLESv2.cpp b/src/OpenGL/libGLESv2/libGLESv2.cpp
index fed303f..209853a 100644
--- a/src/OpenGL/libGLESv2/libGLESv2.cpp
+++ b/src/OpenGL/libGLESv2/libGLESv2.cpp
@@ -802,6 +802,11 @@
 		return error(GL_INVALID_VALUE);
 	}
 
+	if(!IsCompressed(format))
+	{
+		return error(GL_INVALID_ENUM);
+	}
+
 	if(imageSize != gl::ComputeCompressedSize(width, height, format))
 	{
 		return error(GL_INVALID_VALUE);