More robust "are we running in a TTY" check

Previously the return value of the setfont program was used, which sets
the font used in a Linux console.  In a PTY (e.g. terminal emulator), it
generally fails, but who knows, it might not.

This commit makes the check a little closer to the source of the
information, by checking what device stdin is connected to: is it one of
/dev/tty* or something else?  If it's /dev/tty*, we're in a console and
deploy the font hack.

May help with karlstav/cava#68.

cava.c

@@ -552,10 +552,14 @@ Options:\n\
 		pr =  fftw_plan_dft_r2c_1d(M, inr, *outr, FFTW_MEASURE); 
 	}
 
-
-	virt = system("setfont cava.psf  >/dev/null 2>&1");
-	if (virt == 0) system("setterm -blank 0");
-
+    // Check if we're running in a console
+    virt = strncmp(ttyname(0), "/dev/tty", 8);
+
+    if (virt == 0) {
+        system("setfont cava.psf  >/dev/null 2>&1");
+        system("echo yep > /tmp/testing123");
+        system("setterm -blank 0");
+    }
 
 	//output: start ncurses mode
 	if (om == 1 || om ==  2) {