Add checks for imagepath before invoking frisbeelauncher. Avoids

obscure errors since we allow the path to be set to null. Setting the
path to null via the web page is probably not a good idea, but I just
did that by accident and noticed what happened ...

tbsetup/os_load.in

@@ -275,6 +275,18 @@ foreach my $node (@nodes) {
     my $defosid   = $imageid_row{'default_osid'};
     my $shared    = $imageid_row{'shared'};
 
+    #
+    # Check for a few errors early!
+    #
+    if (!defined($imagepath)) {
+	die("*** $0:\n".
+	    "    There is no filename associated with $imageid!\n");
+    }
+    if (! -R $imagepath) {
+	die("*** $0:\n".
+	    "    $imagepath does not exists or cannot be read!\n");
+    }
+
     #
     # 0 means load the entire disk.
     #