eShims::strftime(): Ensure callable from format map is a closure

Otherwise, one might encounter `is_callable("dd")` and a
`function dd(…)` is defined, leading to that function being called
instead of the string being used directly as the replacement.

e107_handlers/Shims/Internal/StrftimeTrait.php

@@ -39,7 +39,7 @@ trait StrftimeTrait
 
 		foreach (self::getFormatMap() as $strftime_key => $date_format_key)
 		{
-			if (is_callable($date_format_key))
+			if (!is_string($date_format_key) && is_callable($date_format_key))
 			{
 				$replacement = self::escapeDateTimePattern($date_format_key($datetime));
 			}