Fix segfaults when using PC outside a section

src/asm/rpn.c

@@ -106,7 +106,10 @@ void rpn_Symbol(struct Expression *expr, char *tzSym)
 {
 	struct sSymbol *sym = sym_FindSymbol(tzSym);
 
-	if (!sym || !sym_IsConstant(sym)) {
+	if (sym == pPCSymbol && !pPCSymbol->pSection) {
+		yyerror("PC has no value outside a section");
+		rpn_Number(expr, 0);
+	} else if (!sym || !sym_IsConstant(sym)) {
 		rpn_Init(expr);
 		expr->isSymbol = true;
 

src/asm/symbol.c

@@ -230,7 +230,9 @@ uint32_t sym_GetConstantValue(char const *s)
 	struct sSymbol const *psym = sym_FindSymbol(s);
 
 	if (psym == pPCSymbol) {
-		if (pCurrentSection->nOrg == -1)
+		if (!pCurrentSection)
+			yyerror("PC has no value outside a section");
+		else if (pCurrentSection->nOrg == -1)
 			yyerror("Expected constant PC but section is not fixed");
 		else
 			return sym_GetValue(psym);

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

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

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

@@ -0,0 +1,3 @@
+ERROR: assert@-no-sect.asm(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: if@-no-sect.asm(1):
+    PC has no value outside a section
+error: Assembly aborted (1 errors)!