libsanitizer: fix SVACE warnings.

libsanitizer: fix SVACE warnings.

  * lsan_thread.cc: return value of a function '__lsan::CurrentThreadContext'
    is dereferenced without checking.
  * sanitizer_libc.cc: casting a signed value which has type 'char' to a
    bigger unsigned integer type 'unsigned int' while initializing a
    variable.
  * sanitizer_libignore.cc: constructor may not initialize class members of
    '__sanitizer::LibIgnore'.
  * sanitizer_printf.cc: 'minimal_num_length' with type 'u8', is promoted to
    type 'int' 32b in 'minimal_num_length - pos', then sign-extended to type
    'unsigned long' 64b.
  * sanitizer_symbolizer_posix_libcdep.cc: after having been compared to NULL
    value, pointer (...)->path is passed as 1st parameter in call to function
    '__sanitizer::LLVMSymbolizer::LLVMSymbolizer', where it is dereferenced.

Change-Id: I9ebcd68362d68be8d738f4b9d5eaad3fae796f6a
Signed-off-by: Andrey Drobyshev <a.drobyshev@samsung.com>