[PATCH] Compile without warning with gcc's -Wtype-limits, -Wempty-body

Hi,

the attached trivial patch allows to compile with -Wtype-limits
-Wempty-body (or -Wextra -Wno-unused-parameter -Wno-sign-compare
-Wno-missing-field-initializers).

As the two fixes seem harmless, that seems to be a good idea. And the
recent "bug" (its not really that, but ...) in walsender.c shows that at
least -Wtype-limits is a sensible warning.

Independently from this patch, should we add -Wtype-limits to the
default parameters?

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
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