Fixes #36 Command buffer overflow with SHT2x

[vcolella]

This fixes #36. Problem was a buffer overflow when splitting the T and RH commands for SHT2x.

[hmueller01]

Ok, this works on ESP8266 as there is a 4 byte alignment and if cmd is 1,2,3 or 4 does not overwrite other used memory.
Thanks for the finding. But I would implement this in another way ...

[hmueller01]

+    // read T from SHT2x Sensor
     // Upper byte is T for SHT2x Sensors
     cmd[0] = mI2cCommand >> 8;
-    // Lower byte is RH for SHT2x Sensors
-    cmd[1] = mI2cCommand & 0xff;
-
-    // read T from SHT2x Sensor
     if (!readFromI2c(mWire, mI2cAddress, cmd, mCmd_Size, data,
                      EXPECTED_DATA_SIZE / 2, mDuration)) {
       DEBUG_SHT("SHT2x readFromI2c(T) false\n");
       return false;
+
     }
+
     // read RH from SHT2x Sensor
-    if (!readFromI2c(mWire, mI2cAddress, &cmd[1], mCmd_Size, &data[3],
+    // Lower byte is RH for SHT2x Sensors
+    cmd[0] = mI2cCommand & 0xff;
+    if (!readFromI2c(mWire, mI2cAddress, cmd, mCmd_Size, &data[3],
                      EXPECTED_DATA_SIZE / 2, mDuration)) {

[vcolella]

Ok, this works on ESP8266 as there is a 4 byte alignment and if cmd is 1,2,3 or 4 does not overwrite other used memory.

Ah, now it makes sense why it failed for me, I was testing with an Atmega328p.

Regarding you implementation, I guess it does make more sense to just reuse cmd[0]. I'll update the PR.