mesa: Avoid read of uninitialized variable

The is_color_attachement variable is later read when handling two
separate error cases, where only one of the cases results in the
variable being initialized.

This can be avoided by giving the variable a safe default value.

Coverity-Id: 1398631
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit 88becf73022d780cfd0d7dbc5bb3911f8b0d2b11)
diff --git a/src/mesa/main/fbobject.c b/src/mesa/main/fbobject.c
index 044bd63..8148dac 100644
--- a/src/mesa/main/fbobject.c
+++ b/src/mesa/main/fbobject.c
@@ -3628,7 +3628,7 @@
                                            GLint *params, const char *caller)
 {
    const struct gl_renderbuffer_attachment *att;
-   bool is_color_attachment;
+   bool is_color_attachment = false;
    GLenum err;
 
    /* The error code for an attachment type of GL_NONE differs between APIs.