patch 8.1.0053: first argument of 'completefunc' has inconsistent type

Problem:    The first argument given to 'completefunc' can be Number or
            String, depending on the value.
Solution:   Avoid guessing the type of an argument, use typval_T in the
            callers of call_vim_function(). (Ozaki Kiichi, closes #2993)
diff --git a/src/normal.c b/src/normal.c
index a01a434..4d51c33 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -2219,7 +2219,7 @@
 op_function(oparg_T *oap UNUSED)
 {
 #ifdef FEAT_EVAL
-    char_u	*(argv[1]);
+    typval_T	argv[2];
 # ifdef FEAT_VIRTUALEDIT
     int		save_virtual_op = virtual_op;
 # endif
@@ -2235,12 +2235,14 @@
 	    /* Exclude the end position. */
 	    decl(&curbuf->b_op_end);
 
+	argv[0].v_type = VAR_STRING;
 	if (oap->block_mode)
-	    argv[0] = (char_u *)"block";
+	    argv[0].vval.v_string = (char_u *)"block";
 	else if (oap->motion_type == MLINE)
-	    argv[0] = (char_u *)"line";
+	    argv[0].vval.v_string = (char_u *)"line";
 	else
-	    argv[0] = (char_u *)"char";
+	    argv[0].vval.v_string = (char_u *)"char";
+	argv[1].v_type = VAR_UNKNOWN;
 
 # ifdef FEAT_VIRTUALEDIT
 	/* Reset virtual_op so that 'virtualedit' can be changed in the