private boolean checkValidSubroutine(Address entryPoint, boolean allowExistingInstructions) {
		return checkValidSubroutine(entryPoint, allowExistingInstructions, true);
	}
Check if there is a valid subroutine starting at the target address.
It does this by following the flow until a terminator is reached.
If a bad instruction is hit or it does not flow well, then return
false.

@param entryPoint address to check

@return true if entryPoint is the probable subroutine start
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/util/PseudoDisassembler.java