parse_repoclosure: skip empty lines

Looks like we can get empty lines in the `dnf repoclosure` output
sometimes (not sure why). They break things, so we'll skip them.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

rmdepcheck.py

@@ -74,6 +74,8 @@ def parse_repoclosure(rc: str) -> list[DepTuple]:
     out = []
     pkg = None
     for line in rc.splitlines():
+        if not line.strip():
+            continue
         if line.strip().startswith("package:"):
             # package, repo
             elems = line.split()

tests/testdata/test_parse_repoclosure.txt

@@ -7,4 +7,5 @@ package: python3-wxnatpy-0.4.0-13.fc42.noarch from baserepo0
 package: python3-x3dh-1.0.4-3.fc43.noarch from baserepo1
   unresolved deps (1):
     python3.14dist(pydantic) >= 1.7.4
+
 Error: Repoclosure ended with unresolved dependencies (3148) across 832 packages.