SL-1130 Prevent crash on mMatrix

indra/llrender/llrender.cpp

@@ -1458,9 +1458,15 @@ void LLRender::matrixMode(U32 mode)
 	if (mode == MM_TEXTURE)
 	{
 		mode = MM_TEXTURE0 + gGL.getCurrentTexUnitIndex();
+		if (mode > MM_TEXTURE3)
+		{
+			// getCurrentTexUnitIndex() can go as high as 32 (LL_NUM_TEXTURE_LAYERS)
+			// Large value will result in a crash at mMatrix
+			LL_WARNS_ONCE() << "Attempted to assign matrix mode out of bounds: " << mode << LL_ENDL;
+			mode = MM_TEXTURE0;
+		}
 	}
 
-	llassert(mode < NUM_MATRIX_MODES);
 	mMatrixMode = mode;
 }