Reset tess.numVertexes in the end of RB_EndSurface.

This gives us more consistent state and  avoids potentially unnecessary draw calls due to RB_CheckOverflow.

src/engine/renderer/tr_shade.c

@@ -1015,6 +1015,7 @@ void RB_EndSurface( void ) {
 	}
 	// clear shader so we can tell we don't have any unclosed surfaces
 	tess.numIndexes = 0;
+    tess.numVertexes = 0;
 
 	GLimp_LogComment( "----------\n" );
 }