BUG#12929345 : Execution aborts without any messages (Windows only)

This patch corrects an unsafe string concatenation for a Windows-specific
code segment. The symptoms were, under certain conditions like specifying
the location of my-print-defaults and the basedir, and run on a release
build, the client would exit without printing any messages.

client/mysql_plugin.c

@@ -846,12 +846,19 @@ static int process_options(int argc, char *argv[], char *operation)
   {
     i= (int)strlength(opt_basedir);
     if (opt_basedir[i-1] != FN_LIBCHAR || opt_basedir[i-1] != FN_LIBCHAR2)
+    {
+      char buff[FN_REFLEN];
+      
+      strncpy(buff, opt_basedir, sizeof(buff) - 1);
 #ifdef __WIN__
-      if (opt_basedir[i-1] != '/')
-        strcat(opt_basedir, "//");
+      strncat(buff, "/", sizeof(buff) - 1);
 #else
-      strcat(opt_basedir, FN_DIRSEP);
+      strncat(buff, FN_DIRSEP, sizeof(buff) - 1);
 #endif
+      buff[sizeof(buff) - 1]= 0;
+      my_delete(opt_basedir, MYF(0));
+      opt_basedir= my_strdup(buff, MYF(MY_FAE));
+    }
   }
   
   /*