chan_ooh323: Fix cppcheck warnings

Fix cppcheck warnings about redundant conditions and possible
null pointer usage

ASTERISK-27793 #close
Reported by: Ilya Shipitsin
Tested by: Ilya Shipitsin

Change-Id: I0b31933b062a23331dbac9a82b8bcfe345f406f6

addons/ooh323c/src/context.c

@@ -164,6 +164,7 @@ OOCTXT* newContext ()
          /* ASN1CRTFREE0 (pctxt); */
 	 ast_free(pctxt);
          pctxt = 0;
+         return (pctxt);
       }
       pctxt->flags |= ASN1DYNCTXT;
    }