Fix T43834: Text object looses one char after another by entering/leaving edit mode.

Own mistake in refactoring of `BLI_strncpy_wchar_as_utf8()`, if given size was exactly
the one needed, we'd lost last char (off-by-one error).

Many thanks to plasmasolutions (Thomas Beck) who found the issue and did
all the investigation work here!

1 files changed, 3 insertions, 3 deletions

diff --git a/source/blender/blenlib/intern/string_utf8.c b/source/blender/blenlib/intern/string_utf8.c
index c93c3cf628c..67ff532cb6f 100644
--- a/source/blender/blenlib/intern/string_utf8.c
+++ b/source/blender/blenlib/intern/string_utf8.c
@@ -249,7 +249,7 @@ char *BLI_strncat_utf8(char *__restrict dst, const char *__restrict src, size_t
 size_t BLI_strncpy_wchar_as_utf8(char *__restrict dst, const wchar_t *__restrict src, const size_t maxncpy)
 {
 	const size_t maxlen = maxncpy - 1;
-	const size_t maxlen_secured = ((int)maxlen - 6) < 0 ? 0 : maxlen - 6;  /* 6 is max utf8 length of an unicode char. */
+	const int64_t maxlen_secured = (int64_t)maxlen - 6;  /* 6 is max utf8 length of an unicode char. */
 	size_t len = 0;
 
 	BLI_assert(maxncpy != 0);
@@ -258,7 +258,7 @@ size_t BLI_strncpy_wchar_as_utf8(char *__restrict dst, const wchar_t *__restrict
 	memset(dst, 0xff, sizeof(*dst) * maxncpy);
 #endif
 
-	while (*src && len < maxlen_secured) {
+	while (*src && len <= maxlen_secured) {
 		len += BLI_str_utf8_from_unicode((unsigned int)*src++, dst + len);
 	}
 
@@ -268,7 +268,7 @@ size_t BLI_strncpy_wchar_as_utf8(char *__restrict dst, const wchar_t *__restrict
 		char t[6];
 		size_t l = BLI_str_utf8_from_unicode((unsigned int)*src++, t);
 		BLI_assert(l <= 6);
-		if (len + l >= maxlen) {
+		if (len + l > maxlen) {
 			break;
 		}
 		memcpy(dst + len, t, l);