Fix incorrect line numbers with some IF blocks

If a line ended with a string's closing quote, or a newline escape, then
skipping over that line via IF/ELIF/ELSE would fail to count that line,
offsetting the rest of the file.
I have no idea why but for some reason 9829be1 changed *specifically*
`if_skip_to_else` to have incorrect behavior on string endings. The incorrect
behavior on newline escapes seems to have been here since the beginning.
Also added a test to check for both of those behaviors in both functions.

Honestly, it baffles me that nobody ever noticed. I didn't until I started
working on #395.

src/asm/asmy.y

@@ -354,20 +354,14 @@ static void if_skip_to_else(void)
 				src++;
 			}
 		} else {
-			switch (*src) {
-			case '\\':
-				src += 2;
-				break;
-
-			case '\"':
-				src += 2;
+			if (*src == '\"') {
 				inString = false;
-				break;
-
-			default:
-				src++;
-				break;
+			} else if (*src == '\\') {
+				/* Escaped quotes don't end the string */
+				if (*++src != '\"')
+					src--;
 			}
+			src++;
 		}
 	}
 
@@ -405,21 +399,14 @@ static void if_skip_to_endc(void)
 				src++;
 			}
 		} else {
-			switch (*src) {
-
-			case '\\':
-				src += 2;
-				break;
-
-			case '\"':
-				src++;
+			if (*src == '\"') {
 				inString = false;
-				break;
-
-			default:
-				src++;
-				break;
+			} else if (*src == '\\') {
+				/* Escaped quotes don't end the string */
+				if (*++src != '\"')
+					src--;
 			}
+			src++;
 		}
 	}
 

test/asm/correct-line-number.asm

@@ -0,0 +1,11 @@
+IF 0
+	"\
+	"
+ELIF 1
+	WARN "Am I geting ahead of myself?"
+ELSE
+	"\
+	"
+ENDC
+
+WARN "Hopefully not."

test/asm/correct-line-number.out

@@ -0,0 +1,4 @@
+warning: correct-line-number.asm(5):
+    Am I geting ahead of myself?
+warning: correct-line-number.asm(11):
+    Hopefully not.

test/asm/correct-line-number.out.pipe

@@ -0,0 +1,4 @@
+warning: -(5):
+    Am I geting ahead of myself?
+warning: -(11):
+    Hopefully not.

test/asm/multiple-charmaps.out

@@ -1,6 +1,6 @@
 warning: multiple-charmaps.asm(75):
     Using 'charmap' within a section when the current charmap is 'main' is deprecated
-ERROR: multiple-charmaps.asm(100) -> new_(5):
+ERROR: multiple-charmaps.asm(100) -> new_(6):
     Charmap 'map1' already exists
 ERROR: multiple-charmaps.asm(102) -> set_(2):
     Charmap 'map5' doesn't exist

test/asm/multiple-charmaps.out.pipe

@@ -1,6 +1,6 @@
 warning: -(75):
     Using 'charmap' within a section when the current charmap is 'main' is deprecated
-ERROR: -(100) -> new_(5):
+ERROR: -(100) -> new_(6):
     Charmap 'map1' already exists
 ERROR: -(102) -> set_(2):
     Charmap 'map5' doesn't exist