detect/content: account for distance variables

Under some cases (below), the depth and offset values are used
twice. This commit disregards the distance variable (if any), when
computing the final depth.

These rules are logically equivalent::
1. alert tcp any any -> any 8080 (msg:"distance name"; flow:to_server; content:"Authorization:"; content:"5f71ycy"; distance:0; byte_extract:1,0,option_len,string,relative; content:!"|38|"; distance:option_len; within:1; content:"|37|"; distance:-1; within:1; content:"|49|"; distance:option_len; within:1; sid:1;)
2. alert tcp any any -> any 8080 (msg:"distance number"; flow:to_server; content:"Authorization:"; content:"5f71ycy"; distance:0; byte_extract:1,0,option_len,string,relative; content:!"|38|"; distance:7; within:1; content:"|37|"; distance:-1; within:1; content:"|49|"; distance:option_len; within:1; sid:2;)

The differences:
Rule 1: content:!"|38|"; distance:option_len; within:1; //option_len == 7

Rule 2: content:!"|38|"; distance:7; within:1;

Without this commit, rule 2 triggers an alert but rule 1 doesn't.

Issue: 7390

src/detect-content.c

@@ -601,7 +601,8 @@ static void PropagateLimits(Signature *s, SigMatch *sm_head)
                             VALIDATE(depth + cd->within + dist >= 0 &&
                                      depth + cd->within + dist <= UINT16_MAX);
                             depth = cd->depth = (uint16_t)(depth + cd->within + dist);
-                        } else {
+                        } else if ((cd->flags & DETECT_CONTENT_DISTANCE_VAR) == 0) {
+                            // we cannot know the depth yet if it comes from a var
                             SCLogDebug("offset %u + cd->within %u", offset, cd->within);
                             VALIDATE(depth + cd->within >= 0 && depth + cd->within <= UINT16_MAX);
                             depth = cd->depth = (uint16_t)(offset + cd->within);

src/detect-engine-content-inspection.c

@@ -247,8 +247,8 @@ static int DetectEngineContentInspectionInternal(DetectEngineThreadCtx *det_ctx,
             /* If the value came from a variable, make sure to adjust the depth so it's relative
              * to the offset value.
              */
-            if (cd->flags & (DETECT_CONTENT_DISTANCE_VAR|DETECT_CONTENT_OFFSET_VAR|DETECT_CONTENT_DEPTH_VAR)) {
-                 depth += offset;
+            if (cd->flags & (DETECT_CONTENT_OFFSET_VAR | DETECT_CONTENT_DEPTH_VAR)) {
+                depth += offset;
             }
 
             /* update offset with prev_offset if we're searching for