Fixes the issue that line gap may ruin the text layout.

src/fontstash.h

@@ -953,10 +953,11 @@ int fonsAddFontMem(FONScontext* stash, const char* name, unsigned char* data, in
 	// Store normalized line height. The real line height is got
 	// by multiplying the lineh by font size.
 	fons__tt_getFontVMetrics( &font->font, &ascent, &descent, &lineGap);
+	ascent += lineGap;
 	fh = ascent - descent;
 	font->ascender = (float)ascent / (float)fh;
 	font->descender = (float)descent / (float)fh;
-	font->lineh = (float)(fh + lineGap) / (float)fh;
+	font->lineh = font->ascender - font->descender;
 
 	return idx;