Fix Build With M3D Import Only

`M3DWrapper.h` is designed to omit the definition of `class M3DWrapper` if neither M3D import nor M3D export are compiled.
608bccd9cf touched the corresponding preprocessor checks and introduced a bug:
```
#ifndef ASSIMP_BUILD_NO_M3D_IMPORTER
#if !(ASSIMP_BUILD_NO_EXPORT || ASSIMP_BUILD_NO_M3D_EXPORTER)
class M3DWrapper {
```
When compiling
- with M3D import enabled,
- but with either export generally disabled or M3D export disabled specifically,
These checks evaluate to the wrong result and skip the definition, leading to a build failure in dependent code.
```
#if 1 // import enabled
#if !(1 || 1) // export disabled and M3D export disabled
```
This commit fixes the check to compile the definition if neither import is disabled.

code/AssetLib/M3D/M3DWrapper.cpp

@@ -39,8 +39,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 ----------------------------------------------------------------------
 */
-#ifndef ASSIMP_BUILD_NO_M3D_IMPORTER
+#if !defined ASSIMP_BUILD_NO_M3D_IMPORTER || !(defined ASSIMP_BUILD_NO_EXPORT || defined ASSIMP_BUILD_NO_M3D_EXPORTER)
-#if !(ASSIMP_BUILD_NO_EXPORT || ASSIMP_BUILD_NO_M3D_EXPORTER)
 
 #include "M3DWrapper.h"
 
@@ -149,4 +148,3 @@ void M3DWrapper::ClearSave() {
 } // namespace Assimp
 
 #endif
-#endif

code/AssetLib/M3D/M3DWrapper.h

@@ -47,8 +47,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #ifndef AI_M3DWRAPPER_H_INC
 #define AI_M3DWRAPPER_H_INC
 
-#ifndef ASSIMP_BUILD_NO_M3D_IMPORTER
+#if !defined ASSIMP_BUILD_NO_M3D_IMPORTER || !(defined ASSIMP_BUILD_NO_EXPORT || defined ASSIMP_BUILD_NO_M3D_EXPORTER)
-#if !(ASSIMP_BUILD_NO_EXPORT || ASSIMP_BUILD_NO_M3D_EXPORTER)  
 
 #include <memory>
 #include <vector>
@@ -126,7 +125,6 @@ inline m3d_t *M3DWrapper::M3D() const {
 
 } // namespace Assimp
 
-#endif
 #endif // ASSIMP_BUILD_NO_M3D_IMPORTER
 
 #endif // AI_M3DWRAPPER_H_INC