verify-elf(verify_unresolved): correctly treat grep's status, allow standalone use

The pipe (and the function, and the whole script) would fail when the
resulting constructed rpath was empty. But usually at least
$RPM_VERIFY_ELF_LDD_RPATH is not empty, so the bad behavior has not
been observed.

However, when verify-elf is used standalone, $RPM_VERIFY_ELF_LDD_RPATH
is empty indeed, and this improvement becomes important.

Before this improvement:

$ RPM_BUILD_ROOT=/home /usr/lib/rpm/verify-elf /bin/pwd; echo $?
1

After this improvement:

$ VERIFY_ELF_UNRESOLVED=strict RPM_BUILD_ROOT=/home /usr/lib/rpm/verify-elf /bin/pwd; echo $?
0
$ VERIFY_ELF_UNRESOLVED=strict RPM_BUILD_ROOT=/home /usr/lib/rpm/verify-elf /usr/lib64/python3/site-packages/_cffi_backend.cpython-35m.so; echo $?
verify-elf: ERROR: /usr/lib64/python3/site-packages/_cffi_backend.cpython-35m.so: undefined symbol: PyExc_SystemError
....
1

scripts/verify-elf.in

@@ -175,7 +175,7 @@ verify_unresolved()
 	fi
 	rpath="$(printf %s "$rpath" |
 		tr -s '[:space:]' '\n' |
-		grep -v '^$' |
+		{ grep -v '^$' || [ "$?" -eq 1 ]; } |
 		LANG=C uniq |
 		sed -e "s|^|$RPM_BUILD_ROOT&|" |
 		tr -s '[:space:]' : |