[1/2] msvcrt/tests: Add tests for mbstowcs and wcstombs with empty strings.

[Piotr Caban]

Hi,

the patch causes compilation warnings on 64-bit wine.
../../../../wine_src/dlls/msvcrt/tests/string.c: In function 
'test_mbstowcs':
../../../../wine_src/dlls/msvcrt/tests/string.c:1869:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1872:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1887:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1890:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1903:228: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1911:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1932:228: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]
../../../../wine_src/dlls/msvcrt/tests/string.c:1951:123: warning: 
format '%d' expects argument of type 'int', but argument 3 has type 
'size_t {aka long unsigned int}' [-Wformat=]

Thanks,
Piotr