Display an error when ISO is invalid

Previous behavior was to crash the program when an iso file was
unreadable or had 0 length.

This patch has the program display an error dialog and not select the file.

scripts/iso.py

@@ -60,12 +60,20 @@ def iso_size(iso_link):
     return os.path.getsize(iso_link)
 
 
+def is_readable(iso_link):
+    return os.access(iso_link, os.R_OK)
+
+
 def is_bootable(iso_link):
     """
     Check if an ISO has the ability to boot.
     :return: True if ISO is bootable and False if not.
     """
-    iso9660fs = ISO9660(iso_link)
+    try:
+        iso9660fs = ISO9660(iso_link)
+    except IOError as e:
+        log(str(e))
+        raise
     isBootable = iso9660fs.checkISOBootable()
     return bool(isBootable)
 

scripts/isodump3.py

@@ -106,7 +106,10 @@ class ISO9660:
             f = open(isofile, 'rb')
         except(IOError):
             sys.stderr.write("can't open {0}".format(isofile))
-            sys.exit(-1)
+            raise
+
+        if os.path.getsize(isofile) == 0:
+            raise IOError("File {0} appears to be empty".format(isofile))
 
         self.isoFile = f
         self.priVol = None

scripts/mbusb_gui.py

@@ -214,6 +214,22 @@ Are you SURE you want to enable it?",
                                                                   'Img Files(*.img);; All Files(*.*)')[0]
 
         if config.image_path:
+            # sanity checks
+            if not is_readable(config.image_path):
+                QtWidgets.QMessageBox.critical(
+                    self,
+                    "ISO Not readable",
+                    "Sorry, the file \"{0}\" is not readable.".format(config.image_path)
+                )
+                return
+            if iso_size(config.image_path) == 0:
+                QtWidgets.QMessageBox.critical(
+                    self,
+                    "ISO is an empty file",
+                    "Sorry, the file \"{0}\" contains no data.".format(config.image_path)
+                )
+                return
+
             default_dir_path = os.path.dirname(config.image_path)
             gen.write_to_file(preference_file_path, default_dir_path)