Possible fix for the work-around for issue #485

If the new problem reported in comment-293553102 is a
boundary issue (e.g. inptr == inend after skipping the
closing " char), this should solve the problem.

MailKit/Net/Imap/ImapStream.cs

@@ -515,20 +515,20 @@ unsafe ImapToken ReadQuotedStringToken (byte* inbuf, CancellationToken cancellat
 						// skip over closing '"'
 						inptr++;
 
-						// Note: Some IMAP servers do not properly escape double-quotes inside
-						// of a qstring token and so, as an attempt at working around this
-						// problem, check that the closing '"' character is not immediately
-						// followed by any character that we would expect immediately following
-						// a qstring token.
-						//
-						// See https://github.com/jstedfast/MailKit/issues/485 for details.
-						if (inptr < inend && "]) \r\n".IndexOf ((char) *inptr) != -1)
-							break;
-
-						memory.WriteByte ((byte) '"');
-
-						if (inptr < inend)
+						if (inptr < inend) {
+							// Note: Some IMAP servers do not properly escape double-quotes inside
+							// of a qstring token and so, as an attempt at working around this
+							// problem, check that the closing '"' character is not immediately
+							// followed by any character that we would expect immediately following
+							// a qstring token.
+							//
+							// See https://github.com/jstedfast/MailKit/issues/485 for details.
+							if ("]) \r\n".IndexOf ((char) *inptr) != -1)
+								break;
+
+							memory.WriteByte ((byte) '"');
 							continue;
+						}
 					}
 
 					inputIndex = (int) (inptr - inbuf);