false bool is not NULL

There were a few places that used gboolean FALSE
in places where a pointer was expected to mean NULL.
gboolean FALSE being an int 0, this worked.

Both gcc and clang will error if compiled in C23 mode with
this (in C99 until C23, false is a macro constant that
expands to the integer constant 0; false has type int so
this is still legal; in C23 false has type bool and gcc
and clang warn about implicit conversions of bool to
pointers.)

Replace the calls with NULL.

Ping #19116

epan/dissectors/packet-rlogin.c

@@ -256,7 +256,7 @@ static void rlogin_display(rlogin_hash_entry_t *hash_info,
 
 		/* User info tree */
 		user_info_item = proto_tree_add_string_format(rlogin_tree, hf_user_info, tvb,
-		                                              offset, info_len, false,
+		                                              offset, info_len, NULL,
 		                                              "User info (%s)",
 		                                              tvb_format_text(pinfo->pool, tvb, offset, info_len));
 		user_info_tree = proto_item_add_subtree(user_info_item,

epan/dissectors/packet-rpc.c

@@ -2075,7 +2075,7 @@ looks_like_rpc_call(tvbuff_t *tvb, int offset)
 		 * is better than nothing.
 		 */
 		if (rpc_prog_key == 0 || rpc_prog_key == 0xffffffff)
-			return false;
+			return NULL;
 		version = tvb_get_ntohl(tvb, offset+16);
 		if (version > 10)
 			return NULL;

epan/dissectors/packet-saphdb.c

@@ -1249,7 +1249,7 @@ get_saphdb_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int offset, void *data
 static int
 dissect_saphdb_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
 {
-	return dissect_saphdb_message(tvb, pinfo, tree, false);
+	return dissect_saphdb_message(tvb, pinfo, tree, NULL);
 }
 
 static int

extcap_parser.c

@@ -115,7 +115,7 @@ static extcap_token_sentence *extcap_tokenize_sentence(const char *s) {
     unsigned param_type = EXTCAP_PARAM_UNKNOWN;
 
     if (!g_utf8_validate(s, -1, NULL))
-        return false;
+        return NULL;
 
     extcap_token_sentence *rs = g_new0(extcap_token_sentence, 1);
 

wiretap/file_access.c

@@ -2174,7 +2174,7 @@ wtap_dump_init_dumper(int file_type_subtype, wtap_compression_type compression_t
 	if (!wtap_dump_can_open(file_type_subtype)) {
 		/* Invalid type, or type we don't know how to write. */
 		*err = WTAP_ERR_UNWRITABLE_FILE_TYPE;
-		return false;
+		return NULL;
 	}
 
 	/* OK, we know how to write that file type/subtype; can we write

wsutil/tempfile.c

@@ -133,7 +133,7 @@ create_tempdir(const char *parent_dir, const char *tmpl, GError **err)
       g_free(temp_subdir);
       g_set_error_literal(err, G_FILE_ERROR,
           g_file_error_from_errno(errno), g_strerror(errno));
-      return false;
+      return NULL;
   }
 
   return temp_subdir;