svpaint: Change a variable from global to local
svpaint: Change a variable from global to local

This fixes a warning from LGTM:

    Poor global variable name 'rgb'. Prefer longer, descriptive
    names for globals (eg. kMyGlobalConstant, not foo).

Signed-off-by: Stefan Weil <8d4c780fcfdc41841e5070f4c43da8958ba6aec0@weilnetz.de>

UB-Mannheim/tesseract,UB-Mannheim/tesseract,amitdo/tesseract,UB-Mannheim/tesseract,jbarlow83/tesseract,amitdo/tesseract,tesseract-ocr/tesseract,stweil/tesseract,jbarlow83/tesseract,tesseract-ocr/tesseract,stweil/tesseract,tesseract-ocr/tesseract,amitdo/tesseract,stweil/tesseract,UB-Mannheim/tesseract,stweil/tesseract,UB-Mannheim/tesseract,jbarlow83/tesseract,stweil/tesseract,amitdo/tesseract,jbarlow83/tesseract,jbarlow83/tesseract,tesseract-ocr/tesseract,tesseract-ocr/tesseract,amitdo/tesseract