UI: Fix encoder rescaling for streaming

The "rescale" option for streaming in the advanced output settings was
not properly checking the parameter output of sscanf.  sscanf returns
the number of values that were found, not the number of string matches.

obs/window-basic-main-outputs.cpp

@@ -402,7 +402,7 @@ inline void AdvancedOutput::SetupStreaming()
 	unsigned int cx = 0;
 	unsigned int cy = 0;
 
-	if (rescale && sscanf(rescaleRes, "%ux%u", &cx, &cy) != 3) {
+	if (rescale && sscanf(rescaleRes, "%ux%u", &cx, &cy) != 2) {
 		cx = 0;
 		cy = 0;
 	}