cube/char_bigrams: Fix some memory leaks
cube/char_bigrams: Fix some memory leaks

Coverity report:

CID 1164717 (#1 of 1): Resource leak (RESOURCE_LEAK)
10. leaked_storage: Variable upper_32 going out of scope leaks
 the storage it points to.

CID 1164718 (#1 of 1): Resource leak (RESOURCE_LEAK)
10. leaked_storage: Variable lower_32 going out of scope leaks
 the storage it points to.

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

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