[buffer] Add hb_buffer_has_positions()

Fixes https://github.com/harfbuzz/harfbuzz/issues/2716

docs/harfbuzz-sections.txt

@@ -80,6 +80,7 @@ hb_buffer_set_user_data
 hb_buffer_get_user_data
 hb_buffer_get_glyph_infos
 hb_buffer_get_glyph_positions
+hb_buffer_has_positions
 hb_buffer_get_invisible_glyph
 hb_buffer_set_invisible_glyph
 hb_buffer_set_replacement_codepoint

src/hb-buffer.cc

@@ -50,7 +50,7 @@
  * Checks the equality of two #hb_segment_properties_t's.
  *
  * Return value:
- * %true if all properties of @a equal those of @b, false otherwise.
+ * %true if all properties of @a equal those of @b, %false otherwise.
  *
  * Since: 0.9.7
  **/
@@ -1404,6 +1404,25 @@ hb_buffer_get_glyph_positions (hb_buffer_t  *buffer,
   return (hb_glyph_position_t *) buffer->pos;
 }
 
+/**
+ * hb_buffer_has_positions:
+ * @buffer: an #hb_buffer_t.
+ *
+ * Returns whether @buffer has glyph position data.
+ * A buffer gains position data when hb_buffer_get_glyph_positions() is called on it,
+ * and cleared of position data when hb_buffer_clear_contents() is called.
+ *
+ * Return value:
+ * %true if the @buffer has position array, %false otherwise.
+ *
+ * Since: REPLACEME
+ **/
+HB_EXTERN hb_bool_t
+hb_buffer_has_positions (hb_buffer_t  *buffer)
+{
+  return buffer->have_positions;
+}
+
 /**
  * hb_glyph_info_get_glyph_flags:
  * @info: a #hb_glyph_info_t.

src/hb-buffer.h

@@ -447,6 +447,9 @@ HB_EXTERN hb_glyph_position_t *
 hb_buffer_get_glyph_positions (hb_buffer_t  *buffer,
 			       unsigned int *length);
 
+HB_EXTERN hb_bool_t
+hb_buffer_has_positions (hb_buffer_t  *buffer);
+
 
 HB_EXTERN void
 hb_buffer_normalize_glyphs (hb_buffer_t *buffer);