[Indic] For scripts without Half forms, always choose first consonant as base

In such scripts (ie. Khmer), a ZWJ/ZWNJ shouldn't stop the search for
base.  So, instead just choose the first consonant as base directly.

Test sequence:
U+1798,200c,U+17C9,U+17D2,U+179B,U+17C1,U+17C7

src/hb-ot-shape-complex-indic.cc

@@ -352,6 +352,8 @@ initial_reordering_consonant_syllable (const hb_ot_map_t *map, hb_buffer_t *buff
       has_reph = true;
     };
 
+    if (basic_mask_array[HALF])
+    {
       /* -> starting from the end of the syllable, move backwards */
       unsigned int i = end;
       do {
@@ -381,6 +383,15 @@ initial_reordering_consonant_syllable (const hb_ot_map_t *map, hb_buffer_t *buff
 	  if (is_joiner (info[i]))
 	    break;
       } while (i > limit);
+    }
+    else
+    {
+      /* In scripts without half forms (eg. Khmer), the first consonant is always the base. */
+
+      if (!has_reph)
+	base = limit;
+    }
+
     if (base < start)
       base = start; /* Just in case... */