net/textproto: correct documentation of empty line handling

Fixes #32493

Change-Id: I9c93791c4cc5c0c14556802733066407de3181ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/185542
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: qbradq

src/net/textproto/reader.go

@@ -88,7 +88,7 @@ func (r *Reader) readLineSlice() ([]byte, error) {
 // The first call to ReadContinuedLine will return "Line 1 continued..."
 // and the second will return "Line 2".
 //
-// A line consisting of only white space is never continued.
+// Empty lines are never continued.
 //
 func (r *Reader) ReadContinuedLine() (string, error) {
 	line, err := r.readContinuedLineSlice(noValidation)