sv.h: Make SvIsUV() return 1 (rather than 0x80000000) for true condition

This would make it easier to receive the result with `bool` type.

Note that (implicit) casting to C99 `_Bool` automatically converts
any nonzero scalar values to 1, so that this change is technically
not necessary in C99 which perl now requires to compile.  But I think
it will keep the code less surprising.

Author: t-a-k

sv.h

@@ -1045,7 +1045,7 @@ Set the size of the string buffer for the SV. See C<L</SvLEN>>.
 #define BOOL_INTERNALS_sv_isbool_false(sv)      (SvIsCOW_static(sv) && \
         (SvPVX_const(sv) == PL_No))
 
-#define SvIsUV(sv)		(SvFLAGS(sv) & SVf_IVisUV)
+#define SvIsUV(sv)		((SvFLAGS(sv) & SVf_IVisUV) != 0)
 #define SvIsUV_on(sv)		(SvFLAGS(sv) |= SVf_IVisUV)
 #define SvIsUV_off(sv)		(SvFLAGS(sv) &= ~SVf_IVisUV)