Bugfix: Acoustic free surface (merge issue)

src/surface_acoustic_PML.c

@@ -36,6 +36,7 @@ void surface_acoustic_PML(int ndepth, float ** sp){
 
 	j=ndepth;     /* The free surface is located exactly in y=1/2*dh !! */
 	for (i=1;i<=NX;i++){
+        sp[j][i] = 0;
 		for (m=1; m<=fdoh; m++) {
 			sp[j-m][i] = -sp[j+m][i];
 		}