Fix segfaults when using PC outside a section

test/asm/assert@-no-sect.asm

@@ -0,0 +1 @@
+assert @ || 1

test/asm/assert@-no-sect.err

@@ -0,0 +1,3 @@
+ERROR: [email protected](1):
+    PC has no value outside a section
+error: Assembly aborted (1 errors)!

test/asm/if@-no-sect.asm

@@ -0,0 +1,2 @@
+if {@}
+endc

test/asm/if@-no-sect.err

@@ -0,0 +1,3 @@
+ERROR: [email protected](1):
+    PC has no value outside a section
+error: Assembly aborted (1 errors)!