Update make_string util to clean up bad values (#128)

* Update make_string util to clean up bad values
* Order tags alphabetically

exifread/tags/__init__.py

@@ -27,7 +27,7 @@
 
 # To ignore when quick processing
 IGNORE_TAGS = (
-    0x9286,  # user comment
-    0x927C,  # MakerNote Tags
     0x02BC,  # XPM
+    0x927C,  # MakerNote Tags
+    0x9286,  # user comment
 )

exifread/tags/exif.py

@@ -437,10 +437,9 @@
     0xA435: ('LensSerialNumber', ),
     0xA500: ('Gamma', ),
     0xC4A5: ('PrintIM', ),
+    0xC61A: ('BlackLevel', ),
     0xEA1C: ('Padding', ),
     0xEA1D: ('OffsetSchema', ),
     0xFDE8: ('OwnerName', ),
     0xFDE9: ('SerialNumber', ),
-    0xC61A: ('BlackLevel', ),
-
 }

exifread/tags/makernote/nikon.py

@@ -52,7 +52,7 @@ def ev_bias(seq) -> str:
 # Nikon E99x MakerNote Tags
 TAGS_NEW = {
     0x0001: ('MakernoteVersion', make_string),  # Sometimes binary
-    0x0002: ('ISOSetting', make_string),
+    0x0002: ('ISOSetting', ),
     0x0003: ('ColorMode', ),
     0x0004: ('Quality', ),
     0x0005: ('Whitebalance', ),

exifread/utils.py

@@ -3,6 +3,7 @@
 """
 
 from fractions import Fraction
+from typing import Union
 
 
 def ord_(dta):
@@ -11,7 +12,7 @@ def ord_(dta):
     return dta
 
 
-def make_string(seq: bytes) -> str:
+def make_string(seq: Union[bytes, list]) -> str:
     """
     Don't throw an exception when given an out of range character.
     """
@@ -23,10 +24,19 @@ def make_string(seq: bytes) -> str:
                 string += chr(char)
         except TypeError:
             pass
+
     # If no printing chars
     if not string:
-        return str(seq)
-    return string
+        if isinstance(seq, list):
+            string = ''.join(map(str, seq))
+            # Some UserComment lists only contain null bytes, nothing valueable to return
+            if set(string) == {'0'}:
+                return ''
+        else:
+            string = str(seq)
+
+    # Clean undesirable characters on any end
+    return string.strip(' \x00')
 
 
 def make_string_uc(seq) -> str: