Wrap the functions used by image.c in USE_IMAGE

Origin: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=789539

terms.c

@@ -467,6 +467,7 @@ writestr(char *s)
 
 #define MOVE(line,column)       writestr(tgoto(T_cm,column,line));
 
+#ifdef USE_IMAGE
 void
 put_image_osc5379(char *url, int x, int y, int w, int h, int sx, int sy, int sw, int sh, int n_terminal_image)
 {
@@ -720,6 +721,7 @@ get_pixel_per_cell(int *ppc, int *ppl)
 
     return 0;
 }
+#endif				/* USE_IMAGE */
 
 #ifdef USE_MOUSE
 #define W3M_TERM_INFO(name, title, mouse)	name, title, mouse