Clang's static code analysis flagged three warnings against the latest master branch

[kcgen]

https://github.com/dreamer/dosbox-staging/commit/3a219326b6e01175316ff461d41ec3d4ab556572/checks#step:6:110

2019-09-26T07:58:23.6518222Z analyze-build: INFO: /home/runner/work/dosbox-staging/dosbox-staging/src/libs/decoders/internal/ogg/src/bitwise.c:98:12: warning: Array access (via field 'ptr') results in a null pointer dereference
2019-09-26T07:58:23.6519776Z analyze-build: INFO:   b->ptr[0]|=value<<b->endbit;
2019-09-26T07:58:23.6520495Z analyze-build: INFO:      ~~~   ^
2019-09-26T07:58:23.6521232Z analyze-build: INFO: /home/runner/work/dosbox-staging/dosbox-staging/src/libs/decoders/internal/ogg/src/bitwise.c:209:7: warning: 2nd function call argument is an uninitialized value
2019-09-26T07:58:23.6521886Z analyze-build: INFO:       w(b,(unsigned long)(ptr[i]),8);
2019-09-26T07:58:23.6522659Z analyze-build: INFO:       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2019-09-26T07:58:23.6523468Z analyze-build: INFO: /home/runner/work/dosbox-staging/dosbox-staging/src/libs/decoders/internal/ogg/src/bitwise.c:223:7: warning: 2nd function call argument is an uninitialized value
2019-09-26T07:58:23.6524092Z analyze-build: INFO:       w(b,(unsigned long)(ptr[bytes]),bits);
2019-09-26T07:58:23.6524658Z analyze-build: INFO:       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2019-09-26T07:58:23.6525200Z analyze-build: INFO: 3 warnings generated.