glsl: fixed uninitialized pointer

Class "ir_constant" had a bunch of constructors where the pointer member
"array_elements" had not been initialized. This could have lead to unsafe
code if something had tried to write anything to it. This patch fixes
this issue by initializing the pointer to NULL in all the constructors.
This issue was discovered by Coverity.

CID: 401603, 401604, 401605, 401610

Signed-off-by: Jakob Sinclair <sinclair.jakob@openmailbox.org>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
diff --git a/src/compiler/glsl/ir.cpp b/src/compiler/glsl/ir.cpp
index d69ab13..9637d7a 100644
--- a/src/compiler/glsl/ir.cpp
+++ b/src/compiler/glsl/ir.cpp
@@ -663,12 +663,15 @@
 ir_constant::ir_constant()
    : ir_rvalue(ir_type_constant)
 {
+   this->array_elements = NULL;
 }
 
 ir_constant::ir_constant(const struct glsl_type *type,
 			 const ir_constant_data *data)
    : ir_rvalue(ir_type_constant)
 {
+   this->array_elements = NULL;
+
    assert((type->base_type >= GLSL_TYPE_UINT)
 	  && (type->base_type <= GLSL_TYPE_BOOL));
 
@@ -744,6 +747,7 @@
 ir_constant::ir_constant(const ir_constant *c, unsigned i)
    : ir_rvalue(ir_type_constant)
 {
+   this->array_elements = NULL;
    this->type = c->type->get_base_type();
 
    switch (this->type->base_type) {
@@ -759,6 +763,7 @@
 ir_constant::ir_constant(const struct glsl_type *type, exec_list *value_list)
    : ir_rvalue(ir_type_constant)
 {
+   this->array_elements = NULL;
    this->type = type;
 
    assert(type->is_scalar() || type->is_vector() || type->is_matrix()