print: Reject enroll images that can't be matched

If the score of a print matching itself is too low to match, then
reject it. It can never match and it is therefore completely useless.

Also change this into a non-fatal error, the user is free to retry the
enroll step in the hope that more minutiae is found (e.g. longer swipe).

libfprint/fpi-image-device.c

@@ -277,7 +277,7 @@ fpi_image_device_minutiae_detected (GObject *source_object, GAsyncResult *res, g
     {
       print = fp_print_new (device);
       fpi_print_set_type (print, FPI_PRINT_NBIS);
-      if (!fpi_print_add_from_image (print, image, &error))
+      if (!fpi_print_add_from_image (print, image, priv->bz3_threshold, &error))
         {
           g_clear_object (&print);
 

libfprint/fpi-print.c

@@ -154,11 +154,14 @@ minutiae_to_xyt (struct fp_minutiae *minutiae,
 gboolean
 fpi_print_add_from_image (FpPrint *print,
                           FpImage *image,
+                          gint     bz3_threshold,
                           GError **error)
 {
+  g_autofree struct xyt_struct *xyt = NULL;
   GPtrArray *minutiae;
   struct fp_minutiae _minutiae;
-  struct xyt_struct *xyt;
+  gint probe_len;
+  gint score;
 
   if (print->type != FPI_PRINT_NBIS || !image)
     {
@@ -173,8 +176,8 @@ fpi_print_add_from_image (FpPrint *print,
   if (!minutiae || minutiae->len == 0)
     {
       g_set_error (error,
-                   G_IO_ERROR,
+                   FP_DEVICE_RETRY,
-                   G_IO_ERROR_INVALID_DATA,
+                   FP_DEVICE_RETRY_GENERAL,
                    "No minutiae found in image or not yet detected!");
       return FALSE;
     }
@@ -185,7 +188,20 @@ fpi_print_add_from_image (FpPrint *print,
 
   xyt = g_new0 (struct xyt_struct, 1);
   minutiae_to_xyt (&_minutiae, image->width, image->height, xyt);
-  g_ptr_array_add (print->prints, xyt);
+
+  probe_len = bozorth_probe_init (xyt);
+  score = bozorth_to_gallery (probe_len, xyt, xyt);
+  fp_dbg ("self-match score %d/%d", score, bz3_threshold);
+  if (score <= bz3_threshold)
+    {
+      g_set_error (error,
+                   FP_DEVICE_RETRY,
+                   FP_DEVICE_RETRY_GENERAL,
+                   "Not enough minutiae to generate a match!");
+      return FPI_MATCH_SUCCESS;
+    }
+
+  g_ptr_array_add (print->prints, g_steal_pointer (&xyt));
 
   g_clear_object (&print->image);
   print->image = g_object_ref (image);

libfprint/fpi-print.h

@@ -40,6 +40,7 @@ void     fpi_print_set_device_stored (FpPrint *print,
 
 gboolean fpi_print_add_from_image (FpPrint *print,
                                    FpImage *image,
+                                   gint     bz3_threshold,
                                    GError **error);
 
 FpiMatchResult fpi_print_bz3_match (FpPrint * template,