stop warning if an empty body is given to if on a different line

[mycoboco]

Differently from loop statements where continue can be used to replace an empty body, it looks good to allow an empty body to an if statement if the body appears on a different line than the if does.

[mycoboco]

The location of ), not that of if is important when determining "on a different line"; For example,

if (cond1 +
    cond2) ;

this should be considered to have an empty body on the same line as the if statement appears.