LibGfx/TIFF: Don't try to check non-existent values

We were previously only checking the first value, this is wrong for tags
that accept multiple values (e.g. ExtraSamples) and can lead to crashes
on malformed images containing tags with a count of 0.

Userland/Libraries/LibGfx/TIFFGenerator.py

@@ -407,15 +407,19 @@ def generate_tag_handler(tag: Tag) -> str:
     check_value = ''
     if tag.associated_enum is not None:
         not_in_value_list = f"({' && '.join([f'v != {v.value}' for v in tag.associated_enum])})"
-        check_value = fR"""TRY(value[0].visit(
-            []({tiff_type_to_cpp(tag.types[0])} const& v) -> ErrorOr<void> {{
-                if ({not_in_value_list})
-                    return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid value for tag {tag.name}");
-                return {{}};
-            }},
-            [&](auto const&) -> ErrorOr<void> {{
-                VERIFY_NOT_REACHED();
-            }}));
+        check_value = fR"""
+        for (u32 i = 0; i < value.size(); ++i) {{
+            TRY(value[i].visit(
+                []({tiff_type_to_cpp(tag.types[0])} const& v) -> ErrorOr<void> {{
+                    if ({not_in_value_list})
+                        return Error::from_string_literal("TIFFImageDecoderPlugin: Invalid value for tag {tag.name}");
+                    return {{}};
+                }},
+                [&](auto const&) -> ErrorOr<void> {{
+                    VERIFY_NOT_REACHED();
+                }})
+            );
+        }}
 """
 
     output = fR"""    case {tag.id}: