patch 9.0.0634: evaluating "expr" options has more overhead than needed

Problem:    Evaluating "expr" options has more overhead than needed.
Solution:   Use call_simple_func() for 'foldtext', 'includeexpr', 'printexpr',
            "expr" of 'spellsuggest', 'diffexpr', 'patchexpr', 'balloonexpr',
            'formatexpr', 'indentexpr' and 'charconvert'.
diff --git a/src/textformat.c b/src/textformat.c
index 36c6945..dfbeed7 100644
--- a/src/textformat.c
+++ b/src/textformat.c
@@ -938,7 +938,7 @@
     // Evaluate the function.
     if (use_sandbox)
 	++sandbox;
-    r = (int)eval_to_number(fex);
+    r = (int)eval_to_number(fex, TRUE);
     if (use_sandbox)
 	--sandbox;