Prevent obecli crash on exit when obe is not started.

Just starting obecli and then exiting results in segfault.

> user@enc:~/obe-rt# ./obecli
>
> Open Broadcast Encoder command line interface.
> Version 1.0
>
> obecli> quit
> closing obe
> input cancelled
> filters cancelled
> encoders cancelled
> Segmentation fault

This patch fixes the segfault by not allowing pthread_join( NULL, ...) to called.
Fix warnings about possible usage of uninitialized variables.

The warnings were:
> input/sdi/sdi.c: In function 'obe_v210_line_to_nv20_c':
> input/sdi/sdi.c:74:23: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]
> input/sdi/linsys/linsys.c: In function 'capture_data':
> input/sdi/linsys/linsys.c:237:20: warning: 'val' may be used uninitialized in this function [-Wmaybe-uninitialized]
> input/sdi/linsys/linsys.c:215:14: note: 'val' was declared here
Fix C++ warnings related to structure initialization.

The warnings were:
> input/sdi/decklink/decklink.cpp:68:1: warning: narrowing conversion of '-1' from 'int' to 'uint32_t {aka unsigned int}' inside { } is ill-formed in C++11 [-Wnarrowing]
> input/sdi/decklink/decklink.cpp:76:1: warning: narrowing conversion of '-1' from 'int' to 'uint32_t {aka unsigned int}' inside { } is ill-formed in C++11 [-Wnarrowing]
> input/sdi/decklink/decklink.cpp:97:1: warning: narrowing conversion of '-1' from 'int' to 'uint32_t {aka unsigned int}' inside { } is ill-formed in C++11 [-Wnarrowing]
Move functions to prevent unused warnings.
Remove defined but unused variables.
Remove defined but unused functions.
Merge pull request #3 from gfto/fixes

Crash fix and random warning fixes