TrueType typefaces lacking hmtx (horizontal metrics) tables are tolerated if the

incremental interface system is enabaled and an incremental interface
has been specified. This is necessary to support some typefaces passed
from GhostScript.

src/sfnt/ttload.c

@@ -831,6 +831,20 @@
       error = face->goto_table( face, TTAG_hmtx, stream, &table_len );
       if ( error )
       {
+
+#ifdef FT_CONFIG_OPTION_INCREMENTAL
+      /* If this is an incrementally loaded font and there are    */
+      /* overriding metrics tolerate a missing 'hmtx' table.      */
+        if ( face->root.internal->incremental_interface &&
+             face->root.internal->incremental_interface->funcs->
+                 get_glyph_metrics )
+        {
+          face->horizontal.number_Of_HMetrics = 0;
+          error = SFNT_Err_Ok;
+          goto Exit;
+	    }
+#endif
+
         FT_ERROR(( " no horizontal metrics in file!\n" ));
         error = SFNT_Err_Hmtx_Table_Missing;
         goto Exit;