cext: fix compiler warning about sign changing...
cext: fix compiler warning about sign changing
line.len is a Py_ssize_t, and we're casing to size_t (unsigned). On my compiler,
this causes a warning to be emitted:
```
mercurial/cext/manifest.c: In function 'pathlen':
mercurial/cext/manifest.c:48:44: warning: operand of ?: changes signedness from 'Py_ssize_t' {aka 'long int'} to 'long unsigned int' due to unsignedness of other operand [-Wsign-compare]
return (end) ? (size_t)(end - l->start) : l->len;
^~~~~~
```
Differential Revision:
https://phab.mercurial-scm.org/D7913
