oeqa/selftest/image_tyypedep: Avoid undefined variable failure

If something goes wrong with the test, dep can be undefined. Avoid a
traceback for this and handle it more gracefully.

(From OE-Core rev: 0b74cb42aefe5c1b812fd155784e4c6581e26ce2)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/cases/image_typedep.py

@@ -29,11 +29,14 @@ inherit image
         # like CONVERSION_DEPENDS_bz2="somedep"
         result = bitbake('-e emptytest')
 
+        dep = None
         for line in result.output.split('\n'):
             if line.startswith('CONVERSION_DEPENDS_bz2'):
                 dep = line.split('=')[1].strip('"')
                 break
 
+        self.assertIsNotNone(dep, "CONVERSION_DEPENDS_bz2 dependency not found in bitbake -e output")
+
         # Now get the dependency task list and check for the expected task
         # dependency
         bitbake('-g emptytest')