inpcom.c, bug fix, incorrect start value for `prev'

this bug was introduced in the following commit,
which `reused' variable prev,
failing to preserve its initialization value NULL

Author: pnenzi <pnenzi>
Date:   Mon Oct 8 21:10:34 2007 +0000

    Improvements in frontend by Phil Barker

src/frontend/inpcom.c

@@ -629,6 +629,7 @@ inp_readall(FILE *fp, struct line **data, int call_depth, char *dir_name, bool c
         stripped in the following code. */
     inp_stripcomments_deck(working);
 
+    prev = NULL;
     while (working) {
         for (s = working->li_line; (c = *s) != '\0' && c <= ' '; s++)
             ;