Fix: [ICU] crash when trying to break a non-breaking run (#10791)

Clusters from harfbuzz are indexed from the start of the buffer,
not from the start of the run analyzed. This confuses other parts
of the code that do assume they are from the start of the run.

src/gfx_layout_icu.cpp

@@ -208,7 +208,7 @@ void ICURun::Shape(UChar *buff, size_t buff_length) {
 			x_advance = glyph_pos[i].x_advance / FONT_SCALE;
 		}
 
-		this->glyph_to_char.push_back(glyph_info[i].cluster);
+		this->glyph_to_char.push_back(glyph_info[i].cluster - this->start);
 		this->advance.push_back(x_advance);
 		advance += x_advance;
 	}