pretty-print: some more gcc appeasement

(cherry picked from commit b8ac543706)
(cherry picked from commit 275bae99e3)
(cherry picked from commit 9fc7484110)

src/shared/pretty-print.c

@@ -433,9 +433,9 @@ static int guess_type(const char **name, char ***ret_prefixes, bool *ret_is_coll
 
 int conf_files_cat(const char *root, const char *name, CatFlags flags) {
         _cleanup_strv_free_ char **dirs = NULL;
-        char **prefixes = NULL; /* explicit initialization to appease gcc */
-        bool is_collection;
-        const char *extension;
+        char **prefixes = NULL;       /* explicit initialization to appease gcc */
+        bool is_collection = false;   /* explicit initialization to appease gcc */
+        const char *extension = NULL; /* explicit initialization to appease gcc */
         int r;
 
         r = guess_type(&name, &prefixes, &is_collection, &extension);