PSTN: compatibility with old saves with non-PSTN particles layered on…

… top of the starting PSTN particle

P.S. don't use layering, this commit is exactly why it's bad. Layering makes adding new functionality without changing existing behaviour much more difficult, and makes the code more complicated than necessary.

src/simulation/elements/PSTN.cpp

@@ -105,7 +105,8 @@ int Element_PSTN::update(UPDATE_FUNC_ARGS)
 								break;
 							}
 							r = pmap[y+nyy][x+nxx];
-							if((r&0xFF)==PT_PSTN) {
+							if((r&0xFF)==PT_PSTN)
+							{
 								if(parts[r>>8].life)
 									armCount++;
 								else if (armCount)
@@ -119,7 +120,16 @@ int Element_PSTN::update(UPDATE_FUNC_ARGS)
 								{
 									pistonCount += floor((parts[r>>8].temp-268.15)/10);// How many tens of degrees above 0 C, rounded to nearest ten degrees. Can be negative.
 								}
-							} else {
+							}
+							else if (nxx==0 && nyy==0)
+							{
+								// compatibility with BAD THINGS: starting PSTN layered underneath other particles
+								// (in v90, it started scanning from the neighbouring particle, so could not break out of loop at offset=(0,0))
+								pistonCount += floor((parts[i].temp-268.15)/10);
+								continue;
+							}
+							else
+							{
 								pistonEndX = x+nxx;
 								pistonEndY = y+nyy;
 								foundEnd = true;