imapserver: drop SP between body entries in body-type-mpart

This breaks Outlook for iOS.

The new behavior follows Dovecot and the RFC ABNF.

Author: mercata

imapserver/fetch.go

@@ -650,10 +650,9 @@ func writeBodyTypeMpart(enc *imapwire.Encoder, bs *imap.BodyStructureMultiPart,
 	if len(bs.Children) == 0 {
 		panic("imapserver: imap.BodyStructureMultiPart must have at least one child")
 	}
-	for i, child := range bs.Children {
-		if i > 0 {
-			enc.SP()
-		}
+	for _, child := range bs.Children {
+		// ABNF for body-type-mpart doesn't have SP between body entries, and
+		// Outlook for iOS chokes on SP
 		writeBodyStructure(enc, child, extended)
 	}