api/candle : WaitForMultipleObjects returns >= 0

[fenugrec]

minor compilation fix.

MS docs ( https://docs.microsoft.com/en-us/windows/desktop/api/synchapi/nf-synchapi-waitformultipleobjects#return-value ) state that WAIT_OBJECT_0 is "defined as 0", so there is no point in checking for "returnvalue < 0".

This commit silences a compiler warning with gcc.