Fixed sdscat*() bug: read memory error

sds.c

@@ -36,6 +36,7 @@
 #include <ctype.h>
 #include <assert.h>
 #include <limits.h>
+#include <alloca.h>
 #include "sds.h"
 #include "sdsalloc.h"
 
@@ -396,10 +397,15 @@ sds sdsgrowzero(sds s, size_t len) {
  * references must be substituted with the new pointer returned by the call. */
 sds sdscatlen(sds s, const void *t, size_t len) {
     size_t curlen = sdslen(s);
+    char *buf = (char*)t;
 
+    if ((s >= buf && s < buf + len) || (buf >= s && buf < s + curlen)) {
+        buf = alloca(len);
+        memcpy(buf, t, len);
+    }
     s = sdsMakeRoomFor(s,len);
     if (s == NULL) return NULL;
-    memcpy(s+curlen, t, len);
+    memcpy(s+curlen, buf, len);
     sdssetlen(s, curlen+len);
     s[curlen+len] = '\0';
     return s;