fix setuptools_scm LookupError bug

If setuptools_scm is installed but gwinc is not called from the gwinc directory, a LookupError was previously thrown. Now the version is set to '?.?.?' in this case.

gwinc/__init__.py

@@ -10,7 +10,10 @@ try:
 except ModuleNotFoundError:
     try:
         import setuptools_scm
-        __version__ = setuptools_scm.get_version(fallback_version='?.?.?')
+        try:
+            __version__ = setuptools_scm.get_version(fallback_version='?.?.?')
+        except LookupError:
+            __version__ = '?.?.?'
     # FIXME: fallback_version is not available in the buster version
     # (3.2.0-1)
     except (ModuleNotFoundError, TypeError):