utils.h: Add rounding to float conversion to int.

Quote from an audio engineer NR9V:
There is a minor issue of a small amount of crossover distortion though as a result of `ast_slinear_saturated_multiply_float()` not rounding the float. This could result in some quiet but potentially audible distortion artifacts in lower volume parts of the signal. If you have for example a sign wave function with a max amplitude of just a few samples, all samples between -1 and 1 will be truncated to zero, resulting in the waveform no longer being a sine wave and in harmonic distortion.

Resolves: #1176
(cherry picked from commit 55f4294e82)

include/asterisk/utils.h

@@ -490,8 +490,11 @@ static force_inline void ast_slinear_saturated_multiply_float(short *input, floa
 		*input = 32767;
 	else if (res < -32768)
 		*input = -32768;
+	else if (res > 0)
+		*input = (short) (res + 0.5);
 	else
-		*input = (short) res;
+		*input = (short) (res - 0.5);
+
 }
 
 static force_inline void ast_slinear_saturated_divide(short *input, short *value)
@@ -506,8 +509,11 @@ static force_inline void ast_slinear_saturated_divide_float(short *input, float
 		*input = 32767;
 	else if (res < -32768)
 		*input = -32768;
+	else if (res > 0)
+		*input = (short) (res + 0.5);
 	else
-		*input = (short) res;
+		*input = (short) (res - 0.5);
+
 }
 
 #ifdef localtime_r