tag: added function tag_merge_replace()

Like tag_merge(), but can deal with NULL parameters, and frees both
tag objects.

src/cue/cue_tag.c

@@ -173,7 +173,6 @@ cue_tag_file(	FILE* fp,
 {
 	struct tag* cd_tag = NULL;
 	struct tag* track_tag = NULL;
-	struct tag* merge_tag = NULL;
 	struct Cd* cd = NULL;
 
 	if (tnum > 256)
@@ -199,26 +198,7 @@ cue_tag_file(	FILE* fp,
 		cd_delete(cd);
 	}
 
-	if ((cd_tag != NULL) && (track_tag != NULL))
+	return tag_merge_replace(cd_tag, track_tag);
-	{
-		merge_tag = tag_merge(cd_tag, track_tag);
-		tag_free(cd_tag);
-		tag_free(track_tag);
-		return merge_tag;
-	}
-
-	else if (cd_tag != NULL)
-	{
-		return cd_tag;
-	}
-
-	else if (track_tag != NULL)
-	{
-		return track_tag;
-	}
-
-	else
-		return NULL;
 }
 
 struct tag*

src/tag.c

@@ -247,6 +247,22 @@ tag_merge(const struct tag *base, const struct tag *add)
 	return ret;
 }
 
+struct tag *
+tag_merge_replace(struct tag *base, struct tag *add)
+{
+	if (add == NULL)
+		return base;
+
+	if (base == NULL)
+		return add;
+
+	struct tag *tag = tag_merge(base, add);
+	tag_free(base);
+	tag_free(add);
+
+	return tag;
+}
+
 const char *
 tag_get_value(const struct tag *tag, enum tag_type type)
 {

src/tag.h

@@ -165,6 +165,15 @@ struct tag *tag_dup(const struct tag *tag);
 struct tag *
 tag_merge(const struct tag *base, const struct tag *add);
 
+/**
+ * Merges the data from two tags.  Any of the two may be NULL.  Both
+ * are freed by this function.
+ *
+ * @return a newly allocated tag, which must be freed with tag_free()
+ */
+struct tag *
+tag_merge_replace(struct tag *base, struct tag *add);
+
 /**
  * Returns true if the tag contains no items.  This ignores the "time"
  * attribute.