patch 8.2.3619: cannot use a lambda for 'operatorfunc'

Problem:    Cannot use a lambda for 'operatorfunc'.
Solution:   Support using a lambda or partial. (Yegappan Lakshmanan,
            closes #8775)
diff --git a/src/optionstr.c b/src/optionstr.c
index 2c4b2b8..100b0f4 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -2320,10 +2320,18 @@
 # endif
 #endif
 
+    // 'operatorfunc'
+    else if (varp == &p_opfunc)
+    {
+	if (set_operatorfunc_option() == FAIL)
+	    errmsg = e_invarg;
+    }
+
 #ifdef FEAT_QUICKFIX
+    // 'quickfixtextfunc'
     else if (varp == &p_qftf)
     {
-	if (qf_process_qftf_option() == FALSE)
+	if (qf_process_qftf_option() == FAIL)
 	    errmsg = e_invarg;
     }
 #endif