MINOR: h1-htx: Update h1 parsing functions to return result as a size_t

h1 parsing functions (h1_parse_msg_*) returns the number of bytes parsed or
0 if nothing is parsed because an error occurred or some data are
missing. But they never return negative values. Thus, instead of a signed
integer, these function now return a size_t value.

The H1 and FCGI muxes are updated accordingly. Note that h1_parse_msg_data()
has been slightly adapted because the parsing of chunked messages still need
to handle negative values when a parsing error is reported by
h1_parse_chunk_size() or h1_skip_chunk_crlf().

include/haproxy/h1_htx.h

@@ -29,13 +29,13 @@
 #include <haproxy/h1.h>
 #include <haproxy/htx.h>
 
-int h1_parse_msg_hdrs(struct h1m *h1m, union h1_sl *h1sl, struct htx *dsthtx,
-		      struct buffer *srcbuf, size_t ofs, size_t max);
-int h1_parse_msg_data(struct h1m *h1m, struct htx **dsthtx,
-		      struct buffer *srcbuf, size_t ofs, size_t max,
-		      struct buffer *htxbuf);
-int h1_parse_msg_tlrs(struct h1m *h1m, struct htx *dsthtx,
-		      struct buffer *srcbuf, size_t ofs, size_t max);
+size_t h1_parse_msg_hdrs(struct h1m *h1m, union h1_sl *h1sl, struct htx *dsthtx,
+			 struct buffer *srcbuf, size_t ofs, size_t max);
+size_t h1_parse_msg_data(struct h1m *h1m, struct htx **dsthtx,
+			 struct buffer *srcbuf, size_t ofs, size_t max,
+			 struct buffer *htxbuf);
+size_t h1_parse_msg_tlrs(struct h1m *h1m, struct htx *dsthtx,
+			 struct buffer *srcbuf, size_t ofs, size_t max);
 
 /* Returns the URI of an HTX message in the most common format for a H1 peer. It
  * is the path part of an absolute URI when the URI was normalized, ortherwise