Fix return value of `FT_Set_Named_Instance' (#56186).

* src/truetype/ttgxvar.c (TT_Set_Named_Instance): Correctly handle
internal return value -1 of `TT_Set_Var_Design'.

ChangeLog

@@ -1,3 +1,10 @@
+2019-04-22  Werner Lemberg  <wl@gnu.org>
+
+	Fix return value of `FT_Set_Named_Instance' (#56186).
+
+	* src/truetype/ttgxvar.c (TT_Set_Named_Instance): Correctly handle
+	internal return value -1 of `TT_Set_Var_Design'.
+
 2019-04-18  Werner Lemberg  <wl@gnu.org>
 
 	[pcf] Fix handling of undefined glyph (#56067).

docs/CHANGES

@@ -15,6 +15,10 @@ CHANGES BETWEEN 2.10.0 and 2.10.1
     in version 2.10.0 was partially broken, causing premature abortion
     of charmap iteration for many fonts.
 
+  - If  `FT_Set_Named_Instance' was  called  with  the same  arguments
+    twice in a row, the function  returned an incorrect error code the
+    second time.
+
 
 ======================================================================
 

src/truetype/ttgxvar.c

@@ -3080,7 +3080,12 @@
                                  mmvar->num_axis,
                                  named_style->coords );
       if ( error )
+      {
+        /* internal error code -1 means `no change' */
+        if ( error == -1 )
+          error = FT_Err_Ok;
         goto Exit;
+      }
     }
     else
       error = TT_Set_Var_Design( face, 0, NULL );