Check for negative numbers (and zero) before casting in ogrlibkmlfeat…

…ure.cpp:IsPowerOf2().

Coverity - Overflowed return value.

2. overflow: Subtract operation overflows on operands nTmp and 1U.
   	     
CID 164965 (#1 of 1): Overflowed return value (INTEGER_OVERFLOW)

3. overflow_sink: Overflowed or truncated value (or a value computed from an
overflowed or truncated value) nTmp != 0U && (nTmp & nTmp - 1U) == 0U used as
return value.


git-svn-id: https://svn.osgeo.org/gdal/trunk@34758 f0d54148-0727-0410-94bb-9a71ac55c965

gdal/ogr/ogrsf_frmts/libkml/ogrlibkmlfeature.cpp

@@ -164,11 +164,11 @@ static CPLString OGRLIBKMLReplaceLevelXYInURL( const char* pszURL,
 
 static bool IsPowerOf2( int nVal )
 {
+    if( nVal < 1 ) return false;
+
     const unsigned int nTmp = static_cast<unsigned int>(nVal);
 
-    return
-        nTmp != 0 &&
-        (nTmp & (nTmp - 1)) == 0;
+    return (nTmp & (nTmp - 1)) == 0;
 }
 
 /************************************************************************/