Fixed debug extension check

- Check the actual debug extension instead of checking GL 4.0 support;
   it appears that despite having GL 4.0 support, AMD does not implement
   the standard debug extensions even when the *_CONTEXT_DEBUG_BIT_ARB
   flag is set on the context.

 - Also, fixed a place where spaces where used for indents instead of a
   tab.

libobs-opengl/gl-subsystem.c

@@ -73,10 +73,8 @@ static void gl_enable_debug()
 {
 	 /* Perhaps we should create GLEW contexts? */
 
-	if (GLEW_VERSION_4_0)
+	if (GLEW_ARB_debug_output)
 		glDebugMessageCallback(gl_debug_proc, NULL);
-	else if (GLEW_ARB_debug_output) 
-		glDebugMessageCallbackARB(gl_debug_proc, NULL);
 	else {
 		blog(LOG_DEBUG, "Failed to set GL debug callback as it is "
 		                "not supported.");

libobs-opengl/gl-windows.c

@@ -156,7 +156,7 @@ static inline HGLRC gl_init_basic_context(HDC hdc)
 static const int attribs[] = 
 {
 #ifdef _DEBUG
-    WGL_CONTEXT_FLAGS_ARB, WGL_CONTEXT_DEBUG_BIT_ARB,
+	WGL_CONTEXT_FLAGS_ARB, WGL_CONTEXT_DEBUG_BIT_ARB,
 #endif
 	WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
 	0, 0