lib/gis: Fix CWE 398 in user_config (#3874)

The error is: Variable 'len' is modified inside assert statement. Assert statements are removed from release builds so the code inside assert statement is not executed. If the code is needed also in release builds, this is a bug.

lib/gis/user_config.c

@@ -156,7 +156,9 @@ static int _elem_count_split(char *elems)
 
     /* Some basic assertions */
     assert(elems != NULL);
-    assert((len = strlen(elems)) > 0);
+
+    len = strlen(elems);
+    assert(len > 0);
     assert(len < PTRDIFF_MAX);
     assert(*elems != '/');