Handle all-zero versions without crashing

From https://github.com/rpm-software-management/rpm/pull/1184

python-rpm-generators.spec

@@ -1,7 +1,7 @@
 Name:           python-rpm-generators
 Summary:        Dependency generators for Python RPMs
 Version:        11
-Release:        2%{?dist}
+Release:        3%{?dist}
 
 # Originally all those files were part of RPM, so license is kept here
 License:        GPLv2+
@@ -45,6 +45,9 @@ install -Dpm0755 -t %{buildroot}%{_rpmconfigdir} pythondistdeps.py
 %{_rpmconfigdir}/pythondistdeps.py
 
 %changelog
+* Mon Apr 20 2020 Gordon Messmer <gordon.messmer@gmail.com> - 11-3
+- Handle all-zero versions without crashing
+
 * Tue Apr 07 2020 Miro Hrončok <mhroncok@redhat.com> - 11-2
 - Use dynamic %%_prefix value when matching files for python(abi) provides
 - Sync with upstream RPM dist generator

pythondistdeps.py

@@ -44,7 +44,7 @@ class RpmVersion():
             rpm_epoch = str(self.epoch) + ':'
         else:
             rpm_epoch = ''
-        while self.version[-1] == 0:
+        while len(self.version) > 1 and self.version[-1] == 0:
             self.version.pop()
         rpm_version = '.'.join(str(x) for x in self.version)
         if self.pre: