patch 8.1.0439: recursive use of getcmdline() still not protected

Problem:    Recursive use of getcmdline() still not protected.
Solution:   Instead of saving the command buffer when making a call which may
            cause recursiveness, save the buffer when actually being called
            recursively.

src/main.c

@@ -929,6 +929,7 @@ vim_main2(void)
     void
 common_init(mparm_T *paramp)
 {
+    cmdline_init();
 
 #ifdef FEAT_MBYTE
     (void)mb_init();	/* init mb_bytelen_tab[] to ones */