fix BUG-104 by only calling exif auto trans on jpegs, not all images

shared.py

@@ -121,9 +121,13 @@ def SymlinkName(ptype, path, file):
 def GenThumb(fname,auto_rotate):
     try:
         if auto_rotate:
-            # run cmdline util to re-orient jpeg (only changes if needed, and does it losslessly)
-            p = subprocess.run([PA_EXIF_ROTATER,fname] )
-            im=Image.open(fname)
+            im_orig = Image.open(fname)
+            if im_orig.format == 'JPEG':
+                # run cmdline util to re-orient jpeg (only changes if needed, and does it losslessly)
+                p = subprocess.run([PA_EXIF_ROTATER,fname] )
+                im=Image.open(fname)
+            else:
+                im=im_orig
         # if we don't autorotate/touch the original, we still want the thumbnail oriented the right way
         else:
             im_orig = Image.open(fname)