Correct AMSProgressBar sheet presentation oversight!

Co-authored-by: Allen Smith <allen.monroe.smith@gmail.com>

Author: undecoded-coder

trunk/AMSProgressBar/AMSProgressPanel.m

@@ -328,7 +328,7 @@ - (void) showAsSheetForWindow:(NSWindow *)parentWindow
 self.startTime = [NSDate date]; //right now
 runningAsSheet = YES;
 
-[[NSApp mainWindow] beginSheet:dialogWindow completionHandler:nil];
+[parentWindow beginSheet:dialogWindow completionHandler:nil];
 }