Assert that the view has a window

Rebel/NSView+RBLAlignmentAdditions.m

@@ -11,6 +11,7 @@
 @implementation NSView (RBLAlignmentAdditions)
 
 - (NSRect)rbl_viewBackingAlignedRect:(NSRect)rect options:(NSAlignmentOptions)options {
+	NSAssert(self.window != nil, @"View must have a window in order to obtain a rectangle aligned to the backing.");
 	NSRect windowRect = [self convertRect:rect toView:nil];
 	NSRect windowBackingRect = [self backingAlignedRect:windowRect options:options];
 	return [self convertRect:windowBackingRect fromView:nil];