Better display of no expiration dates. Handling of cancel now does'nt overwrite existing expiry date

MacPass/MPDatePickingViewController.h

@@ -13,6 +13,7 @@
 @property (strong,readonly) NSDate *date;
 @property (weak) IBOutlet NSDatePicker *datePicker;
 @property (weak) IBOutlet NSPopUpButton *presetPopupButton;
+@property (assign, readonly) BOOL didCancel;
 
 - (IBAction)useDate:(id)sender;
 - (IBAction)cancel:(id)sender;

MacPass/MPDatePickingViewController.m

@@ -24,6 +24,7 @@ typedef NS_ENUM(NSUInteger, MPDatePreset) {
 @interface MPDatePickingViewController ()
 
 @property (strong) NSDate *date;
+@property (assign) BOOL didCancel;
 
 @end
 
@@ -57,13 +58,14 @@ typedef NS_ENUM(NSUInteger, MPDatePreset) {
 }
 
 - (IBAction)useDate:(id)sender {
+  self.didCancel = NO;
   self.date = [self.datePicker dateValue];
   id target = [NSApp targetForAction:@selector(performClose:)];
   [target performClose:sender];
 }
 
 - (IBAction)cancel:(id)sender {
-  self.date = nil;
+  self.didCancel = YES;
   id target = [NSApp targetForAction:@selector(performClose:)];
   [target performClose:sender];
 }

MacPass/MPInspectorViewController.m

@@ -235,7 +235,9 @@ typedef NS_ENUM(NSUInteger, MPContentTab) {
   }
   if([popover.contentViewController isKindOfClass:[MPDatePickingViewController class]]) {
     MPDatePickingViewController *viewController = (MPDatePickingViewController *)popover.contentViewController;
-    [self _setExpiryDate:viewController.date];
+    if(!viewController.didCancel) {
+      [self _setExpiryDate:viewController.date];
+    }
   }
   self.popover = nil;
 }

MacPass/MPValueTransformerHelper.m

@@ -30,7 +30,7 @@ NSString *const MPExpiryDateValueTransformer = @"com.hicknhack.macpass.kMPExpiry
                                  transformedValueClass:[NSString class]
                     returningTransformedValueWithBlock:^id(id value) {
                       if(![value isKindOfClass:[NSDate class]]) {
-                        return @""; // Wrong input
+                        return NSLocalizedString(@"NO_EXPIRE_DATE_SET","");
                       }
                       static NSDateFormatter *formatter;
                       if(!formatter) {