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Last-ditch maximum size limit for Mines

This makes sure that width * height <= INT_MAX, which it rather needs
to be.  Also a similar check in decode_params when defaulting the
number of mines.

--- a/mines.c

+++ b/mines.c

@@ -12,6 +12,7 @@

 #include <string.h>

 #include <assert.h>

 #include <ctype.h>

+#include <limits.h>

 #include <math.h>

 #include "tree234.h"

@@ -162,7 +163,9 @@

 	params->n = atoi(p);

 	while (*p && (*p == '.' || isdigit((unsigned char)*p))) p++;

     } else {

-	params->n = params->w * params->h / 10;

+        if (params->h > 0 && params->w > 0 &&

+            params->w <= INT_MAX / params->h)

+            params->n = params->w * params->h / 10;

     }

     while (*p) {

@@ -258,6 +261,8 @@

      */

     if (full && params->unique && (params->w <= 2 || params->h <= 2))

 	return "Width and height must both be greater than two";

+    if (params->w > INT_MAX / params->h)

+        return "Width times height must not be unreasonably large";

     if (params->n < 0)

 	return "Mine count may not be negative";

     if (params->n > params->w * params->h - 9)