BUG/MINOR: http: Fix content-length of the default 500 error

96 bytes is announce in the C-L header for a message of body of 97 bytes. This
bug was introduced by the patch 46a030cdd ("CLEANUP: assorted typo fixes in the
code and comments").

This patch must be backported in all versions where the patch above is (the 2.2
for now).
diff --git a/src/http.c b/src/http.c
index 937d4d0..4b1b9cd 100644
--- a/src/http.c
+++ b/src/http.c
@@ -284,7 +284,7 @@
 
 	[HTTP_ERR_500] =
 	"HTTP/1.1 500 Internal Server Error\r\n"
-	"Content-length: 96\r\n"
+	"Content-length: 97\r\n"
 	"Cache-Control: no-cache\r\n"
 	"Content-Type: text/html\r\n"
 	"\r\n"