[LinuxVersion] fix version comparison

LinuxVersion used the assumption that both strings have the same
amount of dot-separated components.
But this is obviously not always the case.
If we can't compare the two strings further they must been equal so far.

emper/lib/LinuxVersion.cpp

@@ -2,7 +2,6 @@
 // Copyright © 2021 Florian Fischer
 #include "lib/LinuxVersion.hpp"
 
-#include <cassert>
 #include <cerrno>
 #include <cstdlib>
 
@@ -47,7 +46,8 @@ auto LinuxVersion::compare(const std::string& s) -> int {
 			dot_pos2 = s.size();
 		} else {
 			dot_pos2 = s.find('.', last_dot_pos2);
-			assert(dot_pos2 != std::string::npos);
+			// The string to compare has less dot-separated components
+			if (dot_pos2 == std::string::npos) return 0;
 		}
 
 		long n1 = checked_strtol(this->version.substr(last_dot_pos, dot_pos - last_dot_pos));

tests/lib/LinuxVersionTest.cpp

@@ -73,3 +73,9 @@ TEST(LinuxVersion, ge) {
 	ASSERT_TRUE(TestLinuxVersion::ge("5.14.0", "4.13"));
 	ASSERT_TRUE(TestLinuxVersion::ge("5.14.0", "5.14.0"));
 }
+
+// NOLINTNEXTLINE(modernize-use-trailing-return-type)
+TEST(LinuxVersion, real_world) {
+	ASSERT_TRUE(TestLinuxVersion::le("5.15.0-0.bpo.2-amd64", "5.15.0"));
+	ASSERT_TRUE(TestLinuxVersion::ge("5.17.0", "5.15.0-0.bpo.2-amd64"));
+}