StringToUTF8(): Don't include the terminating \0 in the returned length.

The majority of Win32 API functions we cover actually behave like this, with
GetCurrentDirectory() being the only exception. And yes, this indeed fixes
some weird bugs in applications that use the Borland VCL library, and EditDisk
in particular.

src/utf.c

@@ -32,7 +32,10 @@ wchar_t* StringToUTF16_VLA(wchar_t *str_w, const char *str_mb, int str_len)
 
 int StringToUTF8(char *str_utf8, const wchar_t *str_w, int str_utf8_len)
 {
-	return WideCharToMultiByte(CP_UTF8, 0, str_w, -1, str_utf8, str_utf8_len, NULL, NULL);
+	int ret = WideCharToMultiByte(
+		CP_UTF8, 0, str_w, -1, str_utf8, str_utf8_len, NULL, NULL
+	);
+	return str_w ? ret - 1 : ret;
 }
 
 int StringToMBFixed(char *str_mb, const wchar_t *str_w, int str_mb_len, int str_w_len)

src/utf.h

@@ -30,7 +30,8 @@ int StringToUTF16(wchar_t *str_w, const char *str_mb, int str_len);
 // [str_mb] (and thus, [str_w]) point to a valid string.
 wchar_t* StringToUTF16_VLA(wchar_t *str_w, const char *str_mb, int str_len);
 
-// Converts a UTF-16 string to UTF-8.
+// Converts a null-terminated UTF-16 string to UTF-8 and returns the
+// converted size excluding the terminating null character.
 // [str_utf8_len] takes the size of [str_utf8] in bytes.
 int StringToUTF8(char *str_utf8, const wchar_t *str_w, int str_utf8_len);
 

src/wrappers.c

@@ -41,7 +41,7 @@ DWORD WINAPI WrapGetString(
 		// Hey, let's be nice and return the _actual_ length.
 		VLA(wchar_t, lpBufferReal_w, ret);
 		func(ret, lpBufferReal_w);
-		ret = StringToUTF8(NULL, lpBufferReal_w, 0);
+		ret = StringToUTF8(NULL, lpBufferReal_w, 0) + 1;
 		VLA_FREE(lpBufferReal_w);
 	}
 	VLA_FREE(lpBuffer_w);