0023787: Eliminate trivial type conversion warnings in MSVC

Explicit type cast added in conversions from double to float in PrsMgr, Select3D, StdPrs, Visual3d, and Voxel.
Minor corrections in ShapeProcess and TCollection.
In Visual3d_ViewManager::ConvertCoord...(), output is initialized by zeros instead of RealLast() in case of failure.
In XmlMXCAFDoc, material density is correctly converted to string when writing to Xml.

src/TCollection/TCollection_ExtendedString.cxx

@@ -166,10 +166,11 @@ TCollection_ExtendedString::TCollection_ExtendedString
       mylength = nbSymbols(astring);
       mystring = Allocate(ROUNDMEM((mylength+1)*2));
       if(!ConvertToUnicode (astring))
+      {
 #ifdef DEB
 	cout <<"UTF8 decoding failure..." <<endl;
 #endif
-      ;
+      }
     }
   }
   else {