librtmp: Avoid an infiniloop setting connection arguments

The exit condition was missing.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
(cherry picked from commit e85d38c20a8893cb59d7c86f74481f2497882196)
Signed-off-by: Timothy Gu <timothygu99@gmail.com>
diff --git a/libavformat/librtmp.c b/libavformat/librtmp.c
index bfa9a71..5a138ad 100644
--- a/libavformat/librtmp.c
+++ b/libavformat/librtmp.c
@@ -193,6 +193,8 @@
 
             if (sep)
                 p = sep + 1;
+            else
+                break;
         }
     }
     if (ctx->playpath) {