Issue #3080: On DJGPP, case_bytes() returns -1 to signal an error if the file
cannot be found.
diff --git a/Python/import.c b/Python/import.c
index abc3906..3b8ce93 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -2084,7 +2084,7 @@
         PyErr_Format(PyExc_NameError,
           "Can't find file for module %.100s\n(filename %.300s)",
           name, buf);
-        return 0;
+        return -1;
     }
     return strncmp(ffblk.ff_name, name, namelen) == 0;