Modernize coding style: Avoid 'continue;' statements where possible.

Modernize coding style: Avoid 'continue;' statements where possible.

* gettext-tools/src/cldr-plurals.c (extract_rules): Use if/else instead of
'continue;'.
* gettext-tools/src/msgfmt.c (msgfmt_operand_list_add_from_directory): Likewise.
* gettext-tools/src/read-po-lex.c (po_gram_lex): Likewise.
* gettext-tools/src/sentence.c (sentence_end): Likewise.
* gettext-tools/src/x-awk.c (extract_parenthesized): Use 'break;' instead of
'continue;'.
* gettext-tools/src/x-c.c (extract_parenthesized): Likewise.
* gettext-tools/src/x-csharp.c (extract_parenthesized): Likewise.
* gettext-tools/src/x-java.c (extract_parenthesized): Likewise.
* gettext-tools/src/x-javascript.c (extract_balanced): Likewise.
* gettext-tools/src/x-lua.c (extract_balanced): Likewise.
* gettext-tools/src/x-modula2.c (extract_parenthesized): Likewise.
* gettext-tools/src/x-php.c (extract_balanced): Likewise.
* gettext-tools/src/x-python.c (extract_balanced): Likewise.
* gettext-tools/src/x-vala.c (extract_balanced): Likewise.
* gettext-tools/src/x-ycp.c (extract_parenthesized): Likewise.