CLEANUP: chunk: Remove duplicated chunk_Xcat implementation

Delegate chunk_istcat, chunk_cat and chunk_strncat to the most generic
chunk_memcat.
diff --git a/include/haproxy/chunk.h b/include/haproxy/chunk.h
index af9ef81..05fd161 100644
--- a/include/haproxy/chunk.h
+++ b/include/haproxy/chunk.h
@@ -107,28 +107,6 @@
 	return 1;
 }
 
-/* appends chunk <src> after <chk>. Returns 0 in case of failure. */
-static inline int chunk_cat(struct buffer *chk, const struct buffer *src)
-{
-	if (unlikely(chk->data + src->data > chk->size))
-		return 0;
-
-	memcpy(chk->area + chk->data, src->area, src->data);
-	chk->data += src->data;
-	return 1;
-}
-
-/* appends ist <src> after <chk>. Returns 0 in case of failure. */
-static inline int chunk_istcat(struct buffer *chk, const struct ist src)
-{
-	if (unlikely(chk->data + src.len > chk->size))
-		return 0;
-
-	memcpy(chk->area + chk->data, src.ptr, src.len);
-	chk->data += src.len;
-	return 1;
-}
-
 /* copies memory area <src> into <chk> for <len> bytes. Returns 0 in
  * case of failure. No trailing zero is added.
  */
@@ -158,6 +136,18 @@
 	return 1;
 }
 
+/* appends ist <src> after <chk>. Returns 0 in case of failure. */
+static inline int chunk_istcat(struct buffer *chk, const struct ist src)
+{
+	return chunk_memcat(chk, istptr(src), istlen(src));
+}
+
+/* appends chunk <src> after <chk>. Returns 0 in case of failure. */
+static inline int chunk_cat(struct buffer *chk, const struct buffer *src)
+{
+	return chunk_memcat(chk, src->area, src->data);
+}
+
 /* copies str into <chk> followed by a trailing zero. Returns 0 in
  * case of failure.
  */
@@ -218,12 +208,7 @@
  */
 static inline int chunk_strncat(struct buffer *chk, const char *str, int nb)
 {
-	if (unlikely(chk->data + nb >= chk->size))
-		return 0;
-
-	memcpy(chk->area + chk->data, str, nb);
-	chk->data += nb;
-	return 1;
+	return chunk_memcat(chk, str, nb);
 }
 
 /* Adds a trailing zero to the current chunk and returns the pointer to the