Fix unsigned integer overflow
Fix unsigned integer overflow

Runtime errors reported by sanitizer:

    src/textord/pithsync.cpp:75:31: runtime error: unsigned integer overflow: 2147483648 + 2147483648 cannot be represented in type 'unsigned int'
    SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/textord/pithsync.cpp:75:31 in
    src/textord/pithsync.cpp:75:43: runtime error: unsigned integer overflow: 0 - 1 cannot be represented in type 'unsigned int'
    SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/textord/pithsync.cpp:75:43 in
    src/textord/pithsync.cpp:125:29: runtime error: unsigned integer overflow: 2147483648 + 2147483648 cannot be represented in type 'unsigned int'
    SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/textord/pithsync.cpp:125:29 in
    src/textord/pithsync.cpp:125:41: runtime error: unsigned integer overflow: 0 - 1 cannot be represented in type 'unsigned int'
    SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior src/textord/pithsync.cpp:125:41 in

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

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