[FIX] Fix possible segfaults in hardsubx_classifier.c due to strdup

[saurabhshah0410]

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strdup will give a segmentation fault if the argument passed to it is
NULL. TessResultIteratorGetUTF8Text returns a char* which can be NULL
and we should not call strdup directly over it. Once we check if the
value returned is not NULL, then we can call strdup.

This also fixes #928.

[cfsmp3]

This doesn't seem correct to me (but the previous one isn't either).

word = strdup(word);

We're losing the original pointer - assuming TessResultIteratorGetUTF8Text() allocates something (I assume it does, but I don't know for sure) we now have a leak.

Using strdup() seems OK to me IF we're going to be messing with the data later, but in this case we should immediately free the tesseract resource after making a copy, since we no longer need it.

Check this out:
http://tess4j.sourceforge.net/docs/docs-1.2/net/sourceforge/tess4j/TessAPI.html#TessBaseAPIGetIterator(net.sourceforge.tess4j.TessAPI.TessBaseAPI)

TessBaseAPIGetIterator

TessAPI.TessResultIterator TessBaseAPIGetIterator(TessAPI.TessBaseAPI handle)

Get a reading-order iterator to the results of LayoutAnalysis and/or Recognize. ****. WARNING! This class points to data held within the TessBaseAPI class, and therefore can only be used while the TessBaseAPI class still exists and has not been subjected to a call of Init, SetImage, Recognize, Clear, End, DetectOS, or anything else that changes the internal PAGE_RES.

[saurabhshah0410]

Oh yes, I didn't realize that I was creating a memory leak. So something like:

char *word_ = TessResultIteratorGetUTF8Text(it, level);
if(word_ == NULL || !strlen(word_))
    continue;
char *word = strdup(word_);
free(word_);

This should work fine right?

[cfsmp3]

No... you can't use free() to unallocate resources returned by TessResultIteratorGetUTF8Text() - take a look at the link I sent. Most likely (but check - I just browsed the API) it's TessResultIteratorDelete.

[cfsmp3]

See comment on the affected line.