sane-tag-music: fix ImageFile to actually support tag deletion

pkgs/additional/sane-scripts/src/sane-tag-music

@@ -511,6 +511,7 @@ class AudioFile(MediaFile):
 
 class ImageFile(MediaFile):
     _exiftool = None  # static, lazy init
+    TAG_PREFIXES = ("", "EXIF:", "PNG:", "XMP:")
 
     def __init__(self, path_: str):
         super().__init__(path_)
@@ -536,10 +537,8 @@ class ImageFile(MediaFile):
             acc += [t for t in new if t not in acc]
         def get_tag(name: str) -> list:
             acc = []
-            append_tags(acc, get_tag_(name))
-            append_tags(acc, get_tag_(f"EXIF:{name}"))
-            append_tags(acc, get_tag_(f"PNG:{name}"))
-            append_tags(acc, get_tag_(f"XMP:{name}"))
+            for prefix in self.TAG_PREFIXES:
+                append_tags(acc, get_tag_(f"{prefix}{name}"))
             return acc
 
         return Tags(
@@ -560,8 +559,12 @@ class ImageFile(MediaFile):
             if len(val) == 1:
                 self.exif[name] = val[0]
             elif len(val) == 0:
-                if name in self.exif:
-                    del self.exif[name]
+                # tags are deleted by setting them "",
+                # and we have to clear all possible tag variants else the deleted one will be re-derived from the others next read.
+                for prefix in self.TAG_PREFIXES:
+                    pname = f"{prefix}{name}"
+                    if pname in self.exif:
+                        self.exif[pname] = ""
             else:
                 logger.warning(f"multiple values for tag {name}: {val!r}")