Fragment output fix

src/OpenGL/compiler/OutputASM.cpp

@@ -3183,7 +3183,8 @@ namespace glsl
 		int registerCount = fragmentOutput->totalRegisterCount();
 		if(requestedLocation < 0)
 		{
-			mContext.error(fragmentOutput->getLine(), "Invalid fragment output location", "fragment shader");
+			ASSERT(requestedLocation == -1); // All other negative values would have been prevented in TParseContext::parseLayoutQualifier
+			return; // No requested location
 		}
 		else if((requestedLocation + registerCount) > sw::RENDERTARGETS)
 		{

src/OpenGL/compiler/ParseHelper.cpp

@@ -2826,7 +2826,7 @@ TLayoutQualifier TParseContext::parseLayoutQualifier(const TString &qualifierTyp
 {
 	TLayoutQualifier qualifier;
 
-	qualifier.location = -1;
+	qualifier.location = -1;  // -1 isn't a valid location, it means the value isn't set. Negative values are checked lower in this function.
 	qualifier.matrixPacking = EmpUnspecified;
 	qualifier.blockStorage = EbsUnspecified;