Don't crash on generating volid without variant

First, this fixes the crash when volume id requires variant uid, but it
is not specified. This happened in buildinstall phase.

When lorax is used, it is run once for each variant, so we can actually
specify the variant and get the correct variant.

When using buildinstall, no volume id will be generated and pungi will
possibly crash later on.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/phases/buildinstall.py

@@ -130,6 +130,7 @@ class BuildinstallPhase(PhaseBase):
 
             if buildinstall_method == "lorax":
                 for variant in self.compose.get_variants(arch=arch, types=['variant']):
+                    volid = get_volid(self.compose, arch, variant=variant, disc_type="boot")
                     commands.append(
                         self._get_lorax_cmd(repo_baseurl, output_dir, variant, arch, buildarch, volid)
                     )

pungi/util.py

@@ -347,9 +347,9 @@ def get_volid(compose, arch, variant=None, escape_spaces=False, disc_type=False)
     # iso = IsoWrapper(logger=compose._logger)
     # volid = iso._truncate_volid(volid)
 
-    if len(volid) > 32:
+    if volid and len(volid) > 32:
         raise ValueError("Could not create volume ID <= 32 characters")
 
-    if escape_spaces:
+    if volid and escape_spaces:
         volid = volid.replace(" ", r"\x20")
     return volid