c-ares segfault in gehostbyname on windows

[Jeremy Leibs]

I'm running c-ares version 1.7.4

I came across a segfault on Windows in ares_gethostbyname.c in "file_lookup"

The basic problem seems to be that PATH_HOSTS isn't initialized.  If the
call to "RegOpenKeyEx" fails, PATH_HOSTS makes it down to "strcat" before
being initialized.  If there are no null characters in the first MAX_PATH
characters, strcat copies off the end of the array and things end up
corrupted.

The valid fix is to clear PATH_HOSTS.  ares_gethostbyaddr contains the same
code, so I fixed it there as well.

I've attached a very simple patch including the changes.

Thanks,
--Jeremy

diff -Naur c-ares.orig/ares_gethostbyaddr.c c-ares/ares_gethostbyaddr.c
--- c-ares.orig/ares_gethostbyaddr.c	2011-08-08 11:21:40.454903562 -0700
+++ c-ares/ares_gethostbyaddr.c	2011-08-08 11:21:43.195528422 -0700
@@ -186,6 +186,7 @@
 
 #ifdef WIN32
   char PATH_HOSTS[MAX_PATH];
+  memset(PATH_HOSTS, 0, MAX_PATH);
   if (IS_NT()) {
     char tmp[MAX_PATH];
     HKEY hkeyHosts;
diff -Naur c-ares.orig/ares_gethostbyname.c c-ares/ares_gethostbyname.c
--- c-ares.orig/ares_gethostbyname.c	2011-08-08 11:21:40.454903562 -0700
+++ c-ares/ares_gethostbyname.c	2011-08-08 11:21:43.195528422 -0700
@@ -344,6 +344,7 @@
 
 #ifdef WIN32
   char PATH_HOSTS[MAX_PATH];
+  memset(PATH_HOSTS, 0, MAX_PATH);
   if (IS_NT()) {
     char tmp[MAX_PATH];
     HKEY hkeyHosts;