Extract check for assembly marker (#3038)

***NO_CI***

Author: josesimoes

src/CLR/Core/TypeSystem.cpp

@@ -1364,19 +1364,32 @@ HRESULT CLR_RT_TypeDescriptor::ExtractTypeIndexFromObject(const CLR_RT_HeapBlock
 //
 static const char c_MARKER_ASSEMBLY_V1[] = "NFMRK1";
 
+bool CLR_RECORD_ASSEMBLY::ValidateMarker() const
+{
+    NATIVE_PROFILE_CLR_CORE();
+
+    // compare the marker
+    return memcmp(marker, c_MARKER_ASSEMBLY_V1, sizeof(c_MARKER_ASSEMBLY_V1)) == 0;
+}
+
 bool CLR_RECORD_ASSEMBLY::GoodHeader() const
 {
     NATIVE_PROFILE_CLR_CORE();
     CLR_RECORD_ASSEMBLY header = *this;
     header.headerCRC = 0;
 
     if (SUPPORT_ComputeCRC(&header, sizeof(header), 0) != this->headerCRC)
+    {
+        // check for a wrong version of the marker
         return false;
+    }
 
     if (this->stringTableVersion != c_CLR_StringTable_Version)
+    {
         return false;
+    }
 
-    return memcmp(marker, c_MARKER_ASSEMBLY_V1, sizeof(c_MARKER_ASSEMBLY_V1)) == 0;
+    return ValidateMarker();
 }
 
 bool CLR_RECORD_ASSEMBLY::GoodAssembly() const

src/CLR/Include/nanoCLR_Types.h

@@ -1011,6 +1011,7 @@ struct CLR_RECORD_ASSEMBLY
 
     bool GoodHeader() const;
     bool GoodAssembly() const;
+    bool ValidateMarker() const;
 
 #if defined(VIRTUAL_DEVICE)
     void ComputeCRC();