Make StableDiffusionProcessingImg2Img.mask_blur a property

Fixes breakage when mask_blur is set after construction.

See https://github.com/Coyote-A/ultimate-upscale-for-automatic1111/issues/111#issuecomment-1652091424

Thanks to Алексей Трофимов and eunnone for reporting the issue.

modules/processing.py

@@ -1232,11 +1232,10 @@ class StableDiffusionProcessingImg2Img(StableDiffusionProcessing):
         self.image_mask = mask
         self.latent_mask = None
         self.mask_for_overlay = None
-        if mask_blur is not None:
-            mask_blur_x = mask_blur
-            mask_blur_y = mask_blur
         self.mask_blur_x = mask_blur_x
         self.mask_blur_y = mask_blur_y
+        if mask_blur is not None:
+            self.mask_blur = mask_blur
         self.inpainting_fill = inpainting_fill
         self.inpaint_full_res = inpaint_full_res
         self.inpaint_full_res_padding = inpaint_full_res_padding
@@ -1246,6 +1245,22 @@ class StableDiffusionProcessingImg2Img(StableDiffusionProcessing):
         self.nmask = None
         self.image_conditioning = None
 
+    @property
+    def mask_blur(self):
+        if self.mask_blur_x == self.mask_blur_y:
+            return self.mask_blur_x
+        return None
+
+    @mask_blur.setter
+    def mask_blur(self, value):
+        self.mask_blur_x = value
+        self.mask_blur_y = value
+
+    @mask_blur.deleter
+    def mask_blur(self):
+        del self.mask_blur_x
+        del self.mask_blur_y
+
     def init(self, all_prompts, all_seeds, all_subseeds):
         self.sampler = sd_samplers.create_sampler(self.sampler_name, self.sd_model)
         crop_region = None