Fix group blocks from dropping errors

[hinshun]

fs a() {
	image string {
		template "{{ invalid }}"
	}
}

group b() {
	image string {
		template "{{ invalid }}"
	}
}

$ hlb run -t a foo.hlb
[+] Building 0.0s (1/1) FINISHED
 => ERROR compiling [a]                                                                                                                                               0.0s
------
 > compiling [a]:
#1 0.000 Caused by: template: foo.hlb:3:3:1: function "invalid" not defined
------

$ hlb run -t b foo.hlb
[+] Building 0.0s (1/1) FINISHED
 => ERROR compiling [b]                                                                                                                                               0.0s
------
 > compiling [b]:
#1 0.000 Caused by: template: foo.hlb:9:3:1: function "invalid" not defined
------