patch 8.0.1505: debugger can't break on a condition

Problem:    Debugger can't break on a condition. (Charles Campbell)
Solution:   Add ":breakadd expr". (Christian Brabandt, closes #859)
diff --git a/src/userfunc.c b/src/userfunc.c
index df72e34..58a6b78 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3085,6 +3085,8 @@
 	    failed = TRUE;
 	    break;
 	}
+	if (has_watchexpr())
+	    dbg_check_breakpoint(eap);
 
 	/* Handle a function returning a Funcref, Dictionary or List. */
 	if (handle_subscript(&arg, &rettv, !eap->skip, TRUE) == FAIL)