Don't try to open the password manager sheet when it's already open. Leaves...

Don't try to open the password manager sheet when it's already open. Leaves dangling references to the released window controller. Issue 5983

sources/PseudoTerminal.m

@@ -4831,6 +4831,10 @@ ITERM_WEAKLY_REFERENCEABLE
 - (void)openPasswordManagerToAccountName:(NSString *)name
                                inSession:(PTYSession *)session {
     DLog(@"openPasswordManagerToAccountName:%@ inSession:%@", name, session);
+    if (_passwordManagerWindowController != nil) {
+        DLog(@"Password manager sheet already open");
+        return;
+    }
     [session reveal];
     DLog(@"Show the password manager as a sheet");
      _passwordManagerWindowController.delegate = nil;
@@ -4851,6 +4855,7 @@ ITERM_WEAKLY_REFERENCEABLE
                              forKey:kCATransactionDisableActions];
         }
         [[_passwordManagerWindowController window] close];
+        _passwordManagerWindowController = nil;
         if (noAnimations) {
             [CATransaction commit];
         }