F3 dataset get_text_header output is bad about segysak

[trhallam]

Can you check this works for you @stevejpurves ?

with open('data/f3_seismic.sgy', mode='rb') as f:
    f.seek(0,0)                 #Locate our position to first byte of file
    data = f.read(3200)         #Read the first 3200 byte from our position
    print(data)
    data = data.decode('ascii') #EBCDIC encoding
    n = 80                      #A textual header is made of 40x80 characters, we split the string every 80 char.
    txt_header=[]               #Empty string list to put the splitted textual header
    for i in range(0, len(data), n):  
        txt_header.append(data[i:i+n])  #splitting the data and put it to txt_header
    for i in range(0,len(txt_header)):
        print(txt_header[i])              #print to see the content

Looks like there might be some funny business happening with segyio.

[trhallam]

patched by 72b0a66, testing required.