Properly orphan polygon index buffer after binding (take 2)

Follow-up to #34088, patch by @oeleo1 from
https://github.com/godotengine/godot/issues/34065#issuecomment-561530896

drivers/gles3/rasterizer_canvas_gles3.cpp

@@ -479,9 +479,8 @@ void RasterizerCanvasGLES3::_draw_generic_indices(GLuint p_primitive, const int
 	glBindBuffer(GL_ARRAY_BUFFER, data.polygon_buffer);
 
 #ifndef GLES_OVER_GL
-	// Orphan the buffers to avoid CPU/GPU sync points caused by glBufferSubData
+	// Orphan the buffer to avoid CPU/GPU sync points caused by glBufferSubData
 	glBufferData(GL_ARRAY_BUFFER, data.polygon_buffer_size, NULL, GL_DYNAMIC_DRAW);
-	glBufferData(GL_ELEMENT_ARRAY_BUFFER, data.polygon_index_buffer_size, NULL, GL_DYNAMIC_DRAW);
 #endif
 
 	uint32_t buffer_ofs = 0;
@@ -532,6 +531,10 @@ void RasterizerCanvasGLES3::_draw_generic_indices(GLuint p_primitive, const int
 
 	//bind the indices buffer.
 	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, data.polygon_index_buffer);
+#ifndef GLES_OVER_GL
+	// Orphan the buffer to avoid CPU/GPU sync points caused by glBufferSubData
+	glBufferData(GL_ELEMENT_ARRAY_BUFFER, data.polygon_index_buffer_size, NULL, GL_DYNAMIC_DRAW);
+#endif
 	glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(int) * p_index_count, p_indices);
 
 	//draw the triangles.