patch 8.1.2046: SafeState may be triggered at the wrong moment

Problem:    SafeState may be triggered at the wrong moment.
Solution:   Move it up higher to after where messages are processed.  Add a
            SafeStateAgain event to tigger there.

src/channel.c

@@ -3593,10 +3593,6 @@ channel_read_json_block(
 
     ch_log(channel, "Blocking read JSON for id %d", id);
 
-    // Not considered a safe state here, since we are processing a JSON message
-    // and parsing other messages while waiting.
-    enter_unsafe_state();
-
     if (id >= 0)
 	channel_add_block_id(chanpart, id);
 
@@ -3666,9 +3662,6 @@ channel_read_json_block(
     if (id >= 0)
 	channel_remove_block_id(chanpart, id);
 
-    // This may trigger a SafeState autocommand.
-    leave_unsafe_state();
-
     return retval;
 }