Improve overflow_underflow_toinf_0 test somewhat

Add test cases that will make explicit ±0.0 and ±INF appear in the AST
output to make sure those cases are handled correctly.

Test/overflow_underflow_toinf_0.frag

@@ -1,12 +1,13 @@
-    #version 320 es
-	precision highp float;
-    out vec4 my_FragColor;
-    void main()
-    {
+#version 320 es
+precision highp float;
+out vec4 my_FragColor;
+void main()
+{
     // GLSL ES 3.00.6 section 4.1.4 Floats:
     // "A value with a magnitude too small to be represented as a mantissa and exponent is converted to zero."
     // 1.0e-50 is small enough that it can't even be stored as subnormal.
     float correct = (1.0e-50 == 0.0) ? 1.0 : 0.0;
-	float correct1 = isinf(1.0e40) ? 1.0 : 0.0;
+    float correct1 = isinf(1.0e40) ? 1.0 : 0.0;
+    vec4 foo = vec4(1.0e-50, -1.0e-50, 1.0e50, -1.0e50);
     my_FragColor = vec4(0.0, correct, correct1, 1.0);
-    }
+}