fastexport: rework newline logic

fastexport: rework newline logic

Newlines should only be added when otherwise the stream would look weird
without them (on blobs), therefore they are the exception.

Flip the logic so they are added, not skipped.

--- a/hgext/fastexport.py	Mon Mar 06 11:27:57 2023 +0000
+++ b/hgext/fastexport.py	Thu Mar 09 13:02:13 2023 -0600
@@ -69,10 +69,10 @@
     return b"refs/heads/" + branch
 
 
-def write_data(buf, data, skip_newline):
+def write_data(buf, data, add_newline=False):
     buf.append(b"data %d\n" % len(data))
     buf.append(data)
-    if not skip_newline or data[-1:] != b"\n":
+    if add_newline or data[-1:] != b"\n":
         buf.append(b"\n")
 
 
@@ -103,7 +103,7 @@
             marks[filerev] = mark
             data = filectx.data()
             buf = [b"blob\n", b"mark :%d\n" % mark]
-            write_data(buf, data, False)
+            write_data(buf, data, True)
             ui.write(*buf, keepprogressbar=True)
             del buf
 
@@ -122,7 +122,7 @@
             convert_to_git_date(ctx.date()),
         ),
     ]
-    write_data(buf, ctx.description(), True)
+    write_data(buf, ctx.description())
     if parents:
         buf.append(b"from :%d\n" % marks[parents[0].hex()])
     if len(parents) == 2: