patch 8.2.4193: cannot use an import in 'charconvert'

Problem:    Cannot use an import in 'charconvert'.
Solution:   Set the script context when evaluating 'charconvert'.  Also expand
            script-local functions in 'charconvert'.
diff --git a/src/optionstr.c b/src/optionstr.c
index 94a1e2a..4aa7cef 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -2329,8 +2329,7 @@
 # ifdef FEAT_POSTSCRIPT
 	    varp == &p_pexpr ||
 # endif
-	    FALSE
-	    )
+	    varp == &p_ccv)
     {
 	char_u	**p_opt = NULL;
 	char_u	*name;
@@ -2369,6 +2368,8 @@
 	if (varp == &p_pexpr)	// 'printexpr'
 	    p_opt = &p_pexpr;
 # endif
+	if (varp == &p_ccv)	// 'charconvert'
+	    p_opt = &p_ccv;
 
 	if (p_opt != NULL)
 	{