The logic for fieldOffsetsArePointers was always reading 32-bit units
even on 64-bits. When fieldOffsetsArePointers is true, fieldOffsets is
declared as int32_t**, so each element *must* be a pointer and therefore
word-sized (64 bits on 64-bit machines). So it doesn't make sense to
only read 32-bit words for this test.
This fixes metadata extraction for 64-bit builds from Il2Cpp versions
5.3.7f1, 5.3.8f2, 5.4.1f1, 5.4.2f2, 5.4.3f1, 5.4.4f1, 5.4.5f1 and
5.4.6f3. Notably, 5.4.0f3 is an unusual outlier which uses int32_t * for
fieldOffsets.
According to the headers I have available, Unity v5.3.2f1 (metadata 19)
lacks the referencedAssemblies{Offset,Count} fields in
Il2CppGlobalMetadataHeader. These appear to have been added some time
between that version and 5.3.3f1 (metadata 20).
Changing these fields makes the Inspector work properly on the output from
Il2Cpp from Unity v5.3.2f1.
