Add 'fall through' comments and fix actual bug

To document when switch cases fall through intentionally, hiding the
warning by GCC at the same time.

Moved the break statement outside of the if conditional in keybindings.c
as I believe this was an actual bug found by GCC's warnings.

src/highlighting.c

@@ -284,10 +284,13 @@ static void parse_keyfile_style(GKeyFile *kf, gchar **list,
 	{
 		case 4:
 			style->italic = utils_atob(list[3]);
+			/* fall through */
 		case 3:
 			style->bold = utils_atob(list[2]);
+			/* fall through */
 		case 2:
 			parse_color(kf, list[1], &style->background);
+			/* fall through */
 		case 1:
 			parse_color(kf, list[0], &style->foreground);
 	}

src/keybindings.c

@@ -2614,8 +2614,8 @@ static gboolean cb_func_document_action(guint key_id)
 			{
 				gint line = sci_get_current_line(doc->editor->sci);
 				editor_toggle_fold(doc->editor, line, 0);
-				break;
 			}
+			break;
 		case GEANY_KEYS_DOCUMENT_REMOVE_MARKERS:
 			on_remove_markers1_activate(NULL, NULL);
 			break;

src/search.c

@@ -1879,6 +1879,7 @@ static void search_finished(GPid child_pid, gint status, gpointer user_data)
 		}
 		case 1:
 			msg = _("No matches found.");
+			/* fall through */
 		default:
 			msgwin_msg_add_string(COLOR_BLUE, -1, NULL, msg);
 			ui_set_statusbar(FALSE, "%s", msg);

src/tools.c

@@ -648,6 +648,7 @@ static void word_count(gchar *text, guint *chars, guint *lines, guint *words)
 		{
 			case '\n':
 				(*lines)++;
+				/* fall through */
 			case '\r':
 			case '\f':
 			case '\t':