Avoid signed overflow during mult-s16-test which intermittently
failed.

Patch by Mark H Weaver <mhw@netris.org>.

--- pulseaudio-5.0/src/tests/mult-s16-test.c.orig	2014-01-23 13:57:55.000000000 -0500
+++ pulseaudio-5.0/src/tests/mult-s16-test.c	2014-10-24 03:13:46.464661815 -0400
@@ -55,7 +55,7 @@
 START_TEST (mult_s16_test) {
     int16_t samples[SAMPLES];
     int32_t volumes[SAMPLES];
-    int32_t sum1 = 0, sum2 = 0;
+    uint32_t sum1 = 0, sum2 = 0;
     int i;
 
     pa_random(samples, sizeof(samples));