lstm: Fix compilation (undeclared 'isnan')
lstm: Fix compilation (undeclared 'isnan')

gcc report:

lstm/lstmrecognizer.cpp:608:47: error: 'isnan' was not declared in this scope
     ASSERT_HOST(!isnan(output.f(t)[null_char_]));

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

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