Return 400 for invalid encodings

libpq will return an error if invalid UTF-8 sequences are used. This
shouldn't be a 500 error.

Author: arp242

go.mod

@@ -36,7 +36,7 @@ require (
 	zgo.at/z18n v0.0.0-20240522230155-4d5af439f8c4
 	zgo.at/zcache/v2 v2.4.1
 	zgo.at/zdb v0.0.0-20250906203858-587e0745f6a8
-	zgo.at/zhttp v0.0.0-20250710171434-88e30454652c
+	zgo.at/zhttp v0.0.0-20251201061952-9a43cabb6d05
 	zgo.at/zli v0.0.0-20250704045222-08cb210424f2
 	zgo.at/zprof v0.0.0-20211217104121-c3c12596d8f0
 	zgo.at/zstd v0.0.0-20251128053228-ec259dea6715