testing needed: only use image loaders which could potentially read file

src/common/image.h

@@ -36,16 +36,17 @@ extern "C" {
 /** return value of image io functions. */
 typedef enum dt_imageio_retval_t
 {
-  DT_IMAGEIO_OK = 0,         // all good :)
-  DT_IMAGEIO_FILE_NOT_FOUND, // file has been lost
-  DT_IMAGEIO_LOAD_FAILED,    // file either corrupted or in a format not supported by the current loader,
-                             // and a more detailed error from among those below is not available.
+  DT_IMAGEIO_OK = 0,              // all good :)
+  DT_IMAGEIO_FILE_NOT_FOUND,      // file has been lost
+  DT_IMAGEIO_LOAD_FAILED,         // file either corrupted or in a format not supported by the current loader,
+                                  // and a more detailed error from among those below is not available.
   DT_IMAGEIO_UNSUPPORTED_FORMAT,  // the file type is not supported; may be one which is a build-time option
   DT_IMAGEIO_UNSUPPORTED_CAMERA,  // the file type is supported, but the camera model is not
   DT_IMAGEIO_UNSUPPORTED_FEATURE, // the file uses an unsupported feature such as compression type
   DT_IMAGEIO_FILE_CORRUPTED,      // invalid data was detected while parsing the file
   DT_IMAGEIO_IOERROR,             // a read error occurred while loading the file
-  DT_IMAGEIO_CACHE_FULL      // buffer allocation for image data failed
+  DT_IMAGEIO_CACHE_FULL,          // buffer allocation for image data failed
+  DT_IMAGEIO_UNRECOGNIZED         // file format was not recognized by loader(s)
 } dt_imageio_retval_t;
 
 typedef enum dt_imageio_write_xmp_t

src/develop/develop.c

@@ -3547,6 +3547,8 @@ void dt_dev_clear_chroma_troubles(dt_develop_t *dev)
 
 void dt_dev_reset_chroma(dt_develop_t *dev)
 {
+  if(!dev)
+    return;
   dt_dev_clear_chroma_troubles(dev);
   dt_dev_chroma_t *chr = &dev->chroma;
   chr->adaptation = NULL;

src/develop/imageop.c

@@ -1185,7 +1185,7 @@ gboolean dt_iop_so_is_hidden(dt_iop_module_so_t *module)
 
 gboolean dt_iop_is_hidden(dt_iop_module_t *module)
 {
-  return dt_iop_so_is_hidden(module->so);
+  return !module || !module->so || dt_iop_so_is_hidden(module->so);
 }
 
 gboolean dt_iop_shown_in_group(dt_iop_module_t *module, uint32_t group)