gdb/testsuite: fix "continue outside of loop" TCL errors

Many test cases had a few lines in the beginning that look like:

if { condition } {
  continue
}

Where conditions varied, but were mostly in the form of ![runto_main] or
[skip_*_tests], making it quite clear that this code block was supposed
to finish the test if it entered the code block. This generates TCL
errors, as most of these tests are not inside loops.  All cases on which
this was an obvious mistake are changed in this patch.

gdb/testsuite/gdb.python/py-framefilter-mi.exp

@@ -22,7 +22,7 @@ set MIFLAGS "-i=mi2"
 
 gdb_exit
 if [mi_gdb_start] {
-    continue
+    return
 }
 
 standard_testfile py-framefilter-mi.c

gdb/testsuite/gdb.python/py-inferior-leak.exp

@@ -23,12 +23,12 @@ standard_testfile
 clean_restart
 
 # Skip all tests if Python scripting is not enabled.
-if { [skip_python_tests] } { continue }
+if { [skip_python_tests] } { return }
 
 # Skip this test if the tracemalloc module is not available.
 if { ![gdb_py_module_available "tracemalloc"] } {
     unsupported "tracemalloc module not available"
-    continue
+    return
 }
 
 set pyfile [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]

gdb/testsuite/gdb.python/py-mi-cmd.exp

@@ -20,7 +20,7 @@ set MIFLAGS "-i=mi"
 
 gdb_exit
 if {[mi_gdb_start]} {
-    continue
+    return
 }
 
 if {[lsearch -exact [mi_get_features] python] < 0} {

gdb/testsuite/gdb.python/py-mi-events.exp

@@ -20,7 +20,7 @@ set MIFLAGS "-i=mi2"
 
 gdb_exit
 if [mi_gdb_start] {
-    continue
+    return
 }
 
 standard_testfile
@@ -31,7 +31,7 @@ if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {deb
     return -1
 }
 
-if { [mi_skip_python_tests] } { continue }
+if { [mi_skip_python_tests] } { return }
 
 set remote_python_file [gdb_remote_download host ${srcdir}/${subdir}/${pyfile}]
 

gdb/testsuite/gdb.python/py-mi-objfile.exp

@@ -20,7 +20,7 @@ set MIFLAGS "-i=mi2"
 
 gdb_exit
 if [mi_gdb_start] {
-    continue
+    return
 }
 
 standard_testfile
@@ -31,7 +31,7 @@ if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {deb
     return -1
 }
 
-if { [mi_skip_python_tests] } { continue }
+if { [mi_skip_python_tests] } { return }
 
 # Make the -gdb.py script available to gdb, it is automagically loaded by gdb.
 # Care is taken to put it in the same directory as the binary so that

gdb/testsuite/gdb.python/py-mi.exp

@@ -21,7 +21,7 @@ set MIFLAGS "-i=mi2"
 
 gdb_exit
 if [mi_gdb_start] {
-    continue
+    return
 }
 
 standard_testfile py-prettyprint.c
@@ -348,7 +348,7 @@ if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}-cxx" \
 }
 
 if [mi_gdb_start] {
-    continue
+    return
 }
 mi_delete_breakpoints
 mi_gdb_reinitialize_dir $srcdir/$subdir