CVE-2025-4878 Initialize pointers where possible

This is mostly mechanical change initializing all the pointers I was able to
find with some grep and manual review of sources and examples.

Used the following greps (which yield some false positives though):

    git grep "    \w* *\* *\w*;$"
    git grep " ssh_session \w*;"
    git grep " ssh_channel \w*;"
    git grep " struct ssh_iterator \*\w*;"
    git grep " ssh_bind \w*;"
    git grep " ssh_key \w*;"
    git grep " ssh_string \w*;"
    git grep " ssh_buffer \w*;"
    git grep " HMACCTX \w*;"
    git grep " SHACTX \w*;"
    grep -rinP '^(?!.*=)\s*(?:\w+\s+)*\w+\s*\*\s*\w+\s*;'

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/getpass.c

@@ -46,7 +46,7 @@
  */
 static int ssh_gets(const char *prompt, char *buf, size_t len, int verify)
 {
-    char *tmp;
+    char *tmp = NULL;
     char *ptr = NULL;
     int ok = 0;
 
@@ -78,7 +78,7 @@ static int ssh_gets(const char *prompt, char *buf, size_t len, int verify)
         }
 
         if (verify) {
-            char *key_string;
+            char *key_string = NULL;
 
             key_string = calloc(1, len);
             if (key_string == NULL) {