fix: prevent ValueError for bizarre empty modules

https://oss-fuzz.com/testcase-detail/4972497630199808

This fuzzed example from oss-fuzz caused this error:

```
        # The first line of modules can lie and say 1 always, even if the first
        # line of code is later. If so, map 1 to the actual first line of the
        # module.
        if env.PYBEHAVIOR.module_firstline_1 and self._multiline:
>           self._multiline[1] = min(self.raw_statements)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^
E           ValueError: min() arg is an empty sequence

coverage/parser.py:206: ValueError
```

Author: nedbat

CHANGES.rst

@@ -33,11 +33,15 @@ Unreleased
 - The C extension module now conforms to `PEP 489`_, closing `issue 1977`_.
   Thanks, `Adam Turner <pull 1978_>`_.
 
+- Fixed a "ValueError: min() arg is an empty sequence" error caused by strange
+  empty modules, found by `oss-fuzz`_.
+
 .. _issue 1746: https://github.com/nedbat/coveragepy/issues/1746
 .. _issue 1977: https://github.com/nedbat/coveragepy/issues/1977
 .. _pull 1978: https://github.com/nedbat/coveragepy/pull/1978
 .. _issue 1980: https://github.com/nedbat/coveragepy/issues/1980
 .. _PEP 489: https://peps.python.org/pep-0489
+.. _oss-fuzz: https://google.github.io/oss-fuzz/
 
 
 .. start-releases

coverage/parser.py

@@ -201,7 +201,7 @@ def _raw_parse(self) -> None:
         # The first line of modules can lie and say 1 always, even if the first
         # line of code is later. If so, map 1 to the actual first line of the
         # module.
-        if env.PYBEHAVIOR.module_firstline_1 and self._multiline:
+        if env.PYBEHAVIOR.module_firstline_1 and self._multiline and self.raw_statements:
             self._multiline[1] = min(self.raw_statements)
 
         self.excluded = self.first_lines(self.excluded)

tests/test_parser.py

@@ -218,6 +218,10 @@ def g2():
             """)
         assert parser.exit_counts() == {1: 1, 2: 1, 3: 1, 5: 1}
 
+    def test_fuzzed_weirdness(self) -> None:
+        # This used to cause a `min of empty sequence` error:
+        self.parse_text("\r\\\n\n\t\t\\\n\n")
+
 
 class ExclusionParserTest(PythonParserTestBase):
     """Tests for the exclusion code in PythonParser."""