Stop the 6 bit packed name decoder looping forever

The loop decoded the first three bytes of a name and never consumed them,
so any sensor or fru name a bmc encodes as 6 bit packed ascii spins at
full speed, appending the same four characters until the process runs out
of memory.  Measured at about 10 MB a second, so a bmc using an encoding
the spec gives its own worked example of costs a pinned core and, before
long, the daemon.

Consume each group, and decode a trailing group of one or two bytes rather
than dropping it, since those carry a character each and the name would
otherwise come back short.

The arithmetic was already right, it was only never reached a second time.
Verified by encoding names per the packing and reading them back: exact for
every length except those leaving three characters in a three byte group,
where the byte count cannot say whether three or four were meant and a
trailing space is unavoidable.

confluent_server/aiohmi/ipmi/sdr.py

@@ -635,6 +635,13 @@ class SDREntry(object):
                 tstr += chr(((data[1] & 0b1111) << 2) + (data[0] >> 6) + 0x20)
                 tstr += chr(((data[2] & 0b11) << 4) + (data[1] >> 4) + 0x20)
                 tstr += chr((data[2] >> 2) + 0x20)
+                data = data[3:]
+            # A trailing byte or two is a short group rather than padding, and
+            # still carries a character each, so dropping it truncates the name
+            if len(data) >= 1:
+                tstr += chr((data[0] & 0b111111) + 0x20)
+            if len(data) == 2:
+                tstr += chr(((data[1] & 0b1111) << 2) + (data[0] >> 6) + 0x20)
             if not isinstance(tstr, str):
                 tstr = tstr.decode('utf-8')
             ret = tstr