Codechange: All ParagraphLayoutFactory::AppendToBuffer assume that the buffer has at least some space.

Assert on that.

src/gfx_layout_fallback.cpp

@@ -96,8 +96,9 @@ public:
  * @param c           The character to add.
  * @return The number of buffer spaces that were used.
  */
-/* static */ size_t FallbackParagraphLayoutFactory::AppendToBuffer(char32_t *buff, const char32_t *buffer_last, char32_t c)
+/* static */ size_t FallbackParagraphLayoutFactory::AppendToBuffer(char32_t *buff, [[maybe_unused]] const char32_t *buffer_last, char32_t c)
 {
+	assert(buff < buffer_last);
 	*buff = c;
 	return 1;
 }

src/gfx_layout_icu.cpp

@@ -522,6 +522,7 @@ std::unique_ptr<const ICUParagraphLayout::Line> ICUParagraphLayout::NextLine(int
 
 /* static */ size_t ICUParagraphLayoutFactory::AppendToBuffer(UChar *buff, const UChar *buffer_last, char32_t c)
 {
+	assert(buff < buffer_last);
 	/* Transform from UTF-32 to internal ICU format of UTF-16. */
 	int32_t length = 0;
 	UErrorCode err = U_ZERO_ERROR;

src/os/macosx/string_osx.h

@@ -63,6 +63,7 @@ public:
 	 */
 	static size_t AppendToBuffer(CharType *buff, const CharType *buffer_last, char32_t c)
 	{
+		assert(buff < buffer_last);
 		if (c >= 0x010000U) {
 			/* Character is encoded using surrogates in UTF-16. */
 			if (buff + 1 <= buffer_last) {

src/os/windows/string_uniscribe.h

@@ -45,6 +45,7 @@ public:
 	*/
 	static size_t AppendToBuffer(CharType *buff, const CharType *buffer_last, char32_t c)
 	{
+		assert(buff < buffer_last);
 		if (c >= 0x010000U) {
 			/* Character is encoded using surrogates in UTF-16. */
 			if (buff + 1 <= buffer_last) {