profile: prevent a crash when line number is unknown

For some unknown reason, `self.lineno` can be None. The previous code crashed in
such case, we now ignore the case, as we do for other error in this function.

We also fallback to using `-1` in the output when this lack of line number
makes it to the display code.

The reason of unknown line-numbers is… unknown.

mercurial/statprof.py

@@ -236,8 +236,8 b' class CodeSite:'
 
     def getsource(self, length):
         if self.source is None:
-            lineno = self.lineno - 1
             try:
+                lineno = self.lineno - 1  # lineno can be None
                 with open(self.path, b'rb') as fp:
                     for i, line in enumerate(fp):
                         if i == lineno:
@@ -773,7 +773,7 b' def display_hotpath(data, fp, limit=0.05'
             codestring = codepattern % (
                 prefix,
                 b'line'.rjust(spacing_len),
-                site.lineno,
+                site.lineno if site.lineno is not None else -1,
                 b''.ljust(max(0, 4 - len(str(site.lineno)))),
                 site.getsource(30),
             )