ParseSpecificCharacterSet: Unknown character set ''. Assuming utf-8 #189

[favadi]

Steps to reproduce:

• acquire a DICOM file with empty SpecificCharacterSet value. This is what it looks like when examined with dcmdump command

  dcmdump sample.dcm | grep -i SpecificCharacterSet
  (0008,0005) CS (no value available)                     #   0, 0 SpecificCharacterSet
  

• try to parse the file with dicom.ParseFile, could be reproduce with following file.

  func TestEmptySpecificCharacterSet(t *testing.T) {
  	const testFile = "./sample.dcm"
  	_, err := dicom.ParseFile(testFile, nil)
  	if err != nil {
  		t.Fatal(err)
  	}
  }
  

Expected behavior:

• test passed

Actual behavior:

• test failed with following error

ParseSpecificCharacterSet: Unknown character set ''. Assuming utf-8

[favadi]

I think it should be fixed with #219.

[favadi]

I confirm that the issue is fixed after #219 merged.