gles2: fail symbol check if lib is missing

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/mapi/es2api/ABI-check

@@ -1,11 +1,19 @@
 #!/bin/sh
+set -eu
 
 # Print defined gl.* functions not in GL ES 3.0 or in
 # (FIXME, none of these should be part of the ABI)
 # GL_EXT_multi_draw_arrays
 # GL_OES_EGL_image
 
-FUNCS=$(nm -D --defined-only ${1-.libs/libGLESv2.so.2} | grep -o 'T gl.*' | cut -c 3- | while read func; do
+LIB=${1-.libs/libGLESv2.so.2}
+
+if ! [ -f "$LIB" ]
+then
+  exit 1
+fi
+
+FUNCS=$(nm -D --defined-only $LIB | grep -o 'T gl.*' | cut -c 3- | while read func; do
 ( grep -q "^$func$" || echo $func )  <<EOF
 glActiveTexture
 glAttachShader