There is a type mismatch for the length parameter of aiString between

the strings used in materials and elsewhere in assimp. Because of this,
in PyAssimp3 strings in materials don't work properly on 64 bits
platforms. This commit adds a StringUInt32 ctypes structure and use it
in GetMaterialProperties as a workaround.

port/PyAssimp3/pyassimp/pyassimp.py

@@ -120,6 +120,19 @@ class aiTuple:
     def __repr__(self):
         return str([x for x in self])
 
+class StringUInt32(ctypes.Structure):
+    """
+    A ctypes structure used for material strings.
+    This is a workaround for a type mismatch for the length field between strings used for materials and elsewhere.
+    """
+    
+    MAXLEN = 1024
+    
+    _fields_ = [
+            ("length", ctypes.c_uint32),
+            ("data", ctypes.c_char*MAXLEN),
+        ]
+
 def _init(self):
     """
     Custom initialize() for C structs, adds safely accessable member functionality.
@@ -253,7 +266,7 @@ def GetMaterialProperties(material):
             value = [x for x in arr]
         elif p.mType == 3: #string can't be an array
             try:
-                value = cast(p.mData, POINTER(structs.String)).contents.data
+                value = cast(p.mData, POINTER(StringUInt32)).contents.data
             except UnicodeDecodeError:
                 print('UnicodeDecodeError reading material property, ignoring.')
                 continue