Fix various issues reported by coverity scan

buffer.c

@@ -118,8 +118,10 @@ bool buffer_vprintf(Buffer *buf, const char *fmt, va_list ap) {
 	va_list ap_save;
 	va_copy(ap_save, ap);
 	int len = vsnprintf(NULL, 0, fmt, ap);
-	if (len == -1 || !buffer_grow(buf, len+1))
+	if (len == -1 || !buffer_grow(buf, len+1)) {
+		va_end(ap_save);
 		return false;
+	}
 	bool ret = vsnprintf(buf->data, len+1, fmt, ap_save) == len;
 	if (ret)
 		buf->len = len+1;

text-util.c

@@ -84,7 +84,6 @@ int text_string_width(const char *data, size_t len) {
 	const char *s = data;
 
 	while (len > 0) {
-		char buf[MB_CUR_MAX];
 		wchar_t wc;
 		size_t wclen = mbrtowc(&wc, s, len, &ps);
 		if (wclen == (size_t)-1 && errno == EILSEQ) {
@@ -98,7 +97,7 @@ int text_string_width(const char *data, size_t len) {
 			/* assume NUL byte will be displayed as ^@ */
 			width += 2;
 			wclen = 1;
-		} else if (buf[0] == '\t') {
+		} else if (wc == L'\t') {
 			width++;
 			wclen = 1;
 		} else {

ui-curses.c

@@ -1103,8 +1103,10 @@ static const char *ui_getkey(Ui *ui) {
 		int tty = open("/dev/tty", O_RDWR);
 		if (tty == -1)
 			goto fatal;
-		if (tty != STDIN_FILENO && dup2(tty, STDIN_FILENO) == -1)
+		if (tty != STDIN_FILENO && dup2(tty, STDIN_FILENO) == -1) {
+			close(tty);
 			goto fatal;
+		}
 		close(tty);
 		termkey_destroy(uic->termkey);
 		if (!(uic->termkey = ui_termkey_new(STDIN_FILENO)))

vis-lua.c

@@ -800,7 +800,7 @@ static int window_index(lua_State *L) {
 		const char *key = lua_tostring(L, 2);
 
 		if (strcmp(key, "viewport") == 0) {
-			Filerange r = win ? view_viewport_get(win->view) : text_range_empty();
+			Filerange r = view_viewport_get(win->view);
 			pushrange(L, &r);
 			return 1;
 		}

vis-menu.c

@@ -458,7 +458,7 @@ run(void) {
 			return EXIT_FAILURE;
 		case CONTROL('M'): /* Return */
 		case CONTROL('J'):
-			if (sel) strncpy(text, sel->text, sizeof text); /* Complete the input first, when hitting return */
+			if (sel) strncpy(text, sel->text, sizeof(text)-1); /* Complete the input first, when hitting return */
 			cursor = strlen(text);
 			match();
 			drawmenu();