common: text: config_utils: make ParseNameValues skip empty strings

[IEncinas10]

$ cat .rules.verible_lint
+always-ff-non-blocking=catch_modifying_assignments:on;
$ verible-verilog-lint file.sv --rules_config_search
E0929 18:52:13.789277   24408 verilog_linter.cc:146] Fatal error: always-ff-non-blocking : unknown parameter; supported parameters are 'catch_modifying_assignments', 'waive_for_locals'

Current configuration parsing hard-fails upon encountering trailing or leading semicolons in the configuration string. Let's make the process more robust and ignore them.