LibVNCClient: fix possible infinite loop

Closes #251
(cherry picked from commit c3115350eb8bb635d0fdb4dbbb0d0541f38ed19c)

krdc/vnc/rfbproto.c

@@ -987,7 +987,7 @@ HandleRFBServerMessage()
 	/* Regardless of cause, do not divide by zero. */
 	linesToRead = bytesPerLine ? (BUFFER_SIZE / bytesPerLine) : 0;
 
-	while (rect.r.h > 0) {
+	while (linesToRead && rect.r.h > 0) {
 	  if (linesToRead > rect.r.h)
 	    linesToRead = rect.r.h;