Fix compiling error

Travis reports these errors:
/home/travis/build/otland/forgottenserver/src/groups.cpp:48:68: error:
‘value’ may be used uninitialized in this function
[-Werror=uninitialized]
/home/travis/build/otland/forgottenserver/src/groups.cpp:47:68: error:
‘value’ may be used uninitialized in this function
[-Werror=uninitialized]
/home/travis/build/otland/forgottenserver/src/groups.cpp:45:52: error:
‘value’ may be used uninitialized in this function
[-Werror=uninitialized]
/home/travis/build/otland/forgottenserver/src/groups.cpp:43:46: error:
‘value’ may be used uninitialized in this function
[-Werror=uninitialized]

This commit might fix it.