[gimp] app: actually resolve the interpreter through extension as last resort.

[Jehan <jehanp src gnome org>]

commit 51a8ff9c377220b1e0cc188d3dc294b232081b24
Author: Jehan <jehan girinstud io>
Date:   Sat Jun 16 01:16:45 2018 +0200

    app: actually resolve the interpreter through extension as last resort.
    
    Current code of gimp_interpreter_db_resolve() was only resolving the
    interpreter by the file extension when the file could not be opened for
    reading or if it was empty/coult not be read. This basically made this
    test completely useless.
    Let's fix this. Now it will be run all the time, but simply at the end,
    if shebang and magic failed.
    
    (cherry picked from commit 8509117fe64eaacb2a040d539f7bd3a5d7ba6e6b)

 app/plug-in/gimpinterpreterdb.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)
---
diff --git a/app/plug-in/gimpinterpreterdb.c b/app/plug-in/gimpinterpreterdb.c
index 1d92247fd3..43696d3be3 100644
--- a/app/plug-in/gimpinterpreterdb.c
+++ b/app/plug-in/gimpinterpreterdb.c
@@ -752,7 +752,7 @@ resolve_magic (GimpInterpreterDB *db,
       list = list->next;
     }
 
-  return resolve_extension (db, program_path);
+  return NULL;
 }
 
 gchar *
@@ -762,8 +762,7 @@ gimp_interpreter_db_resolve (GimpInterpreterDB  *db,
 {
   GFile        *file;
   GInputStream *input;
-  gsize         bytes_read;
-  gchar         buffer[BUFSIZE];
+  gchar        *program = NULL;
 
   g_return_val_if_fail (GIMP_IS_INTERPRETER_DB (db), NULL);
   g_return_val_if_fail (program_path != NULL, NULL);
@@ -775,22 +774,31 @@ gimp_interpreter_db_resolve (GimpInterpreterDB  *db,
   input = G_INPUT_STREAM (g_file_read (file, NULL, NULL));
   g_object_unref (file);
 
-  if (! input)
-    return resolve_extension (db, program_path);
+  if (input)
+    {
+      gsize bytes_read;
+      gchar buffer[BUFSIZE];
 
-  memset (buffer, 0, sizeof (buffer));
-  g_input_stream_read_all (input, buffer,
-                           sizeof (buffer) - 1, /* leave one nul at the end */
-                           &bytes_read, NULL, NULL);
-  g_object_unref (input);
+      memset (buffer, 0, sizeof (buffer));
+      g_input_stream_read_all (input, buffer,
+                               sizeof (buffer) - 1, /* leave one nul at the end */
+                               &bytes_read, NULL, NULL);
+      g_object_unref (input);
+
+      if (bytes_read)
+        {
+          if (bytes_read > 3 && buffer[0] == '#' && buffer[1] == '!')
+            program = resolve_sh_bang (db, program_path, buffer, bytes_read, interp_arg);
 
-  if (bytes_read == 0)
-    return resolve_extension (db, program_path);
+          if (! program)
+            program = resolve_magic (db, program_path, buffer);
+        }
+    }
 
-  if (bytes_read > 3 && buffer[0] == '#' && buffer[1] == '!')
-    return resolve_sh_bang (db, program_path, buffer, bytes_read, interp_arg);
+  if (! program)
+    program = resolve_extension (db, program_path);
 
-  return resolve_magic (db, program_path, buffer);
+  return program;
 }
 
 static void