[gaml] Concatenating a string representing a path causes weird behaviours

[lesquoyb]

Describe the bug
I noticed that when I try to build a path by concatenating components of it on Windows, the string gets interpreted or something and it changes it's content.

To Reproduce
Steps to reproduce the behavior:

1. Run this:

model testpaths

experiment e{
	
	init {
		string s <- "C:\\Users\\baptiste\\gama-capsis\\capsis-tools\\outputs\\output_file" + 1 + ".txt";
		write s;
	}
}

3. Observe that the string printed in the console is:
   C:tiste\gama-capsis!psis-tools\outputs\output_file1.txt
   instead of
   C:\Users\baptiste\gama-capsis\capsis-tools\outputs\output_file1.txt
4. Remove the concatenation:

		string s <- "C:\\Users\\baptiste\\gama-capsis\\capsis-tools\\outputs\\output_file1.txt";

5. Observe that this time the string printed is correct