fix a few Coverity warnings

thirdparty/dxflib_qcad/dl_dxf.cpp

@@ -370,7 +370,7 @@ bool DL_Dxf::getStrippedLine( std::string& s, unsigned int size,
 bool DL_Dxf::stripWhiteSpace( char** s, bool stripSpace )
 {
     // last non-NULL char:
-    std::size_t lastChar = strlen( *s ) - 1;
+    int lastChar = strlen( *s ) - 1;
 
     // Is last character CR or LF?
     while( (lastChar >= 0)

thirdparty/dxflib_qcad/dl_entities.h

@@ -1149,7 +1149,9 @@ struct DXFLIB_EXPORT DL_DimensionData
         style( astyle ),
         angle( aangle ),
         linearFactor( alinearFactor ),
-        dimScale( adimScale )
+        dimScale( adimScale ),
+        arrow1Flipped( false ),
+        arrow2Flipped(false )
     {
     }