Revert "Revert "Require numerator and denominator in auto fraction""

This reverts commit 8fe506e153.

src/hb-ot-shape.cc

@@ -765,6 +765,8 @@ hb_ot_shape_setup_masks_fraction (const hb_ot_shape_context_t *c)
 	     _hb_glyph_info_get_general_category (&info[end]) ==
 	     HB_UNICODE_GENERAL_CATEGORY_DECIMAL_NUMBER)
 	end++;
+      if (start == i || end == i + 1)
+	continue;
 
       buffer->unsafe_to_break (start, end);
 

test/shape/data/in-house/tests/automatic-fractions.tests

@@ -1,3 +1,7 @@
 ../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;;U+0031,U+0032,U+0033,U+2044,U+0034,U+0035,U+0036;[one.numr=0+600|two.numr=1+600|three.numr=2+600|fraction=3+252|four.small=4+600|five.small=5+600|six.small=6+600]
 ../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;--direction=l --script=arab;U+0031,U+0032,U+0033,U+2044,U+0034,U+0035,U+0036;[one.numr=0+600|two.numr=1+600|three.numr=2+600|fraction=3+252|four.small=4+600|five.small=5+600|six.small=6+600]
 ../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;--direction=l;U+0661,U+0662,U+0663,U+2044,U+0664,U+0665,U+0666;[uni0661.numr=0+600|uni0662.numr=1+600|uni0663.numr=2+600|fraction=3+252|uni0664.small=4+600|uni0665.small=5+600|uni0666.small=6+600]
+../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;;U+0031,U+0032,U+0033,U+2044;[one=0+1090|two=1+1090|three=2+1090|fraction=3+252]
+../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;--direction=l;U+0661,U+0662,U+0663,U+2044;[uni0661=0+1200|uni0662=1+1200|uni0663=2+1200|fraction=3+252]
+../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;;U+2044,U+0034,U+0035,U+0036;[fraction=0+252|four=1+1090|five=2+1090|six=3+1090]
+../fonts/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf;--direction=l;U+2044,U+0664,U+0665,U+0666;[fraction=0+252|uni0664=1+1200|uni0665=2+1200|uni0666=3+1200]