glsl2: Initialize ir_instruction::type and ir_rvalue::type.

Top-level instructions now get NULL as their default type (since type is
irrelevant for things like ir_function), while ir_rvalues get error_type
by default.

This should make it easier to tell if we've forgotten to set a type.  It
also fixes some "Conditional jump or move depends on uninitialized
value" errors in valgrind caused by ir_validate examining the type of
top level ir_instructions, which weren't set.

src/glsl/ir.cpp

@@ -26,6 +26,11 @@
 #include "ir_visitor.h"
 #include "glsl_types.h"
 
+ir_rvalue::ir_rvalue()
+{
+   this->type = glsl_type::error_type;
+}
+
 ir_assignment::ir_assignment(ir_rvalue *lhs, ir_rvalue *rhs,
 			     ir_rvalue *condition)
 {