patch 8.2.4125: completion tests fail

Problem:    Completion tests fail.
Solution:   Disable error messages while dereferencing the function name.
diff --git a/src/eval.c b/src/eval.c
index df73ba1..bf65082 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -709,7 +709,9 @@
 
     // The name might be "import.Func" or "Funcref".
     arg = func;
+    ++emsg_off;
     name = deref_function_name(&arg, &tofree, &EVALARG_EVALUATE, FALSE);
+    --emsg_off;
     if (name == NULL)
 	name = func;