gfauto doesn't handle an integer with the minimum possible value properly

[amakin-siru]

If an input shader includes an integer variable with the minimum possible value, gfauto doesn't handle it properly.

The reason for this behavior is that the visitUnaryExpr method in StandardVisitor passes the integer without the sign to the LiteralToUniformReductionOpportunity class and the positive value goes out of range.

Here's a stacktrace which is the result of having the value -2147483648 in one of the unit tests:

java.lang.NumberFormatException: For input string: "2147483648"
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.lang.Integer.parseInt(Integer.java:587)
	at java.lang.Integer.parseInt(Integer.java:615)
	at com.graphicsfuzz.common.ast.expr.IntConstantExpr.getNumericValue(IntConstantExpr.java:48)
	at com.graphicsfuzz.reducer.reductionopportunities.LiteralToUniformReductionOpportunity.applyReductionImpl(LiteralToUniformReductionOpportunity.java:70)
	at com.graphicsfuzz.reducer.reductionopportunities.AbstractReductionOpportunity.applyReduction(AbstractReductionOpportunity.java:39)
	at java.util.ArrayList.forEach(ArrayList.java:1259)
	at com.graphicsfuzz.reducer.reductionopportunities.LiteralToUniformReductionOpportunitiesTest.testReplaceSimpleInt(LiteralToUniformReductionOpportunitiesTest.java:80)

[sneh19337]

I will be working on this