Security fix from PuTTY 0.72 - vulnerability vuln-ssh1-buffer-length-underflow and vuln-ssh1-short-rsa-keys

https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-ssh1-buffer-length-underflow.html
https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-ssh1-short-rsa-keys.html

Source commit: 75699cceda97ae9b4fb2b946a9895be44b4bcdae

source/putty/ssh.c

@@ -4196,8 +4196,11 @@ static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
 	crStop(0);
     }
 
-    s->len = (s->hostkey.bytes > s->servkey.bytes ?
-              s->hostkey.bytes : s->servkey.bytes);
+    s->len = 32;
+    if (s->len < s->hostkey.bytes)
+        s->len = s->hostkey.bytes;
+    if (s->len < s->servkey.bytes)
+        s->len = s->servkey.bytes;
 
     s->rsabuf = snewn(s->len, unsigned char);