watcher: Don't notify watcher if removed FD was not found

This can happen if a stream is used blocking exclusively (the FD is
never registered with watcher, but is removed in the stream's destructor
just in case it ever was - doing this conditionally would require an
additional flag in streams).  There may be no thread reading from
the read end of the notify pipe (e.g. in starter), causing the write
to the notify pipe to block after it's full.  Anyway, doing a relatively
expensive FD update is unnecessary if there were no changes.

Fixes #1453.

src/libstrongswan/processing/watcher.c

@@ -513,6 +513,7 @@ METHOD(watcher_t, remove_, void,
 	private_watcher_t *this, int fd)
 {
 	entry_t *entry, *prev = NULL;
+	bool found = FALSE;
 
 	this->mutex->lock(this->mutex);
 	while (TRUE)
@@ -530,6 +531,7 @@ METHOD(watcher_t, remove_, void,
 					break;
 				}
 				entry = remove_entry(this, entry, prev);
+				found = TRUE;
 				continue;
 			}
 			prev = entry;
@@ -541,8 +543,10 @@ METHOD(watcher_t, remove_, void,
 		}
 		this->condvar->wait(this->condvar, this->mutex);
 	}
-
-	update(this);
+	if (found)
+	{
+		update(this);
+	}
 	this->mutex->unlock(this->mutex);
 }