MissionPlanner reports params written successfully while failed

#### Issue details
MissionPlanner reports that params has been written successfully while it actually failed.
This occurs in 2 cases:
1. When a connection problem occurs, you change a param then "write" it says at 1st param "blabla" failed. And then says "Parameters has been written successfully"
2. When writing an Internal or Read-only param like "MIS_TOTAL", it doesn't send any error at all, but says "Parameters has been written successfully". Do a "refresh params", you'd find that param has not been written.

#### Version
_1.3.68.1_

#### Platform
[ x ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

Start by reproducing the two parameter-write cases described for MissionPlanner 1.3.68.1: a connection failure and an Internal or Read-only parameter such as MIS_TOTAL. Trace how the write result is reported, then verify that failures are surfaced instead of showing success and that a parameter refresh confirms the outcome.

Written by the indexing model from the issue text.