hpost: fix multipart/form variable name mangeling when field value contains newlines

com='MH3U
pic unrelated
' hpost -u ... -m post com:$com

resulted in wrong field name like:

--HJBOUNDARY
 Content-Disposition: form-data; name="com pic unrelated"

 MH3U
 pic unrelated

rc/bin/hpost

@@ -58,7 +58,7 @@ fn menc {
 	f=$1
 	cr=`{echo x | tr x \015}
 	for(i in $at){
-		k=`{sed 's!:.*$!!' /env/i}
+		k=`{sed 's!:.*$!!; q' /env/i}
 		echo '--'$"f$"cr
 		echo 'Content-Disposition: form-data; name="'$"k'"'$"cr
 		echo $"cr
@@ -66,7 +66,7 @@ fn menc {
 		sed 's!^[^:]+:!!' /env/i
 	}
 	for(i in $af){
-		k=`{sed 's!@.*$!!' /env/i}
+		k=`{sed 's!@.*$!!; q' /env/i}
 		v=`{sed 's!^[^@]+@!!' /env/i}
 		t=`{file -m $v}
 		n=`{basename $v}