EditTextView: Fix redundant initialization

[ma8ma]

無意味な変数初期化を行っているとcppcheckの指摘されたため修正します。

cppcheckのレポート

src/skeleton/editview.cpp:571:24: style: Redundant initialization for 'nlpos'. The initialized value is overwritten before it is read. [redundantInitialization]
        while( ( nlpos = text.rfind( "\n", rpos ) ) != std::string::npos )
                       ^
src/skeleton/editview.cpp:568:22: note: nlpos is initialized
        size_t nlpos = std::string::npos;
                     ^
src/skeleton/editview.cpp:571:24: note: nlpos is overwritten
        while( ( nlpos = text.rfind( "\n", rpos ) ) != std::string::npos )
                       ^